Experience and Foresight

About Calamos Investments

For over 35 years, we have helped investors like you manage and build wealth to meet their long-term individual objectives by working to capitalize on the opportunities of the evolving global marketplace. We launched our first mutual fund in 1985 and our first closed-end fund in 2002. Today, we manage six closed-end funds. These include total-return oriented offerings, which seek current income, with increased emphasis on capital gains potential, and enhanced fixed income offerings, which pursue high current income from income and capital gains. Calamos Global Dynamic Income Fund (CHW) falls into this latter category. Please see page 5 for a more detailed overview of our closed-end offerings.

We are dedicated to helping our clients build and protect wealth. We understand when you entrust us with your assets, you also entrust us with your achievements, goals and aspirations. We believe we best honor this trust by making investment decisions guided by integrity, by discipline, and by our conscientious research.

We believe an active, risk-conscious approach is essential for wealth creation. In the 1970s, we pioneered strategies that seek to participate in equity market upside and mitigate some of the potential risks of equity market volatility. Our investment process seeks to manage risk at multiple levels and draws upon our experience investing through multiple market cycles.

We have a global perspective. We believe globalization offers tremendous opportunities for countries and companies all over the world. In our view, this creates significant opportunities for investors. In our U.S., global and international portfolios, we are seeking to capitalize on the potential growth of the global economy.

We believe there are opportunities in all markets. Our history traces back to the 1970s, a period of significant volatility and economic concerns. We have invested through multiple market cycles, each with its own challenges. Out of this experience comes our belief that the flipside of volatility is opportunity.

JOHN P. CALAMOS, SR.

CEO and Global Co-CIO

Dear Fellow Shareholder:

Welcome to your semiannual report for the six-month period ended April 30, 2015. In this report, you will find commentary from the management team, as well as a listing of portfolio holdings, financial statements and highlights, and detailed information about the Fund’s performance and positioning. I invite you to review not only the commentary for this Fund, but also to discuss with your financial advisor if there are other Calamos funds that could be suitable for your asset allocation.

Calamos Global Dynamic Income Fund (CHW) is an enhanced fixed income fund. We utilize dynamic asset allocation to pursue high current income, while also maintaining a focus on capital gains.

Distribution

During the period, the Fund provided a steady monthly distribution of $0.0700 per share. We believe the Fund’s current annualized distribution rate, which was 9.31%* on a market price basis as of April 30, 2015, was very competitive, given the low interest rates in many segments of the bond market. In our view, the Fund’s distributions illustrate the benefits of a multi-asset class approach and flexible allocation strategy.

We understand that many closed-end fund investors seek steady, predictable distributions instead of distributions that fluctuate. Therefore, this Fund has a level rate distribution policy. As part of this policy, we aim to keep distributions consistent from month to month, and at a level that we believe can be sustained over the long term. In setting the Fund’s distribution rate, the investment management team and the Fund’s Board of Trustees consider the interest rate, market and economic environment. We also factor in our assessment of individual securities and asset classes. (For additional information on our level rate distribution policy, please see “The Calamos Closed-End Funds: An Overview” on page 5 and “Level Rate Distribution Policy” on page 34.)

Market Environment

The MSCI World Index, a measure of stocks from developed markets, returned 5.38% for the six-month period. Growth stocks outperformed, with the MSCI World Growth Index gaining 7.49%. In the U.S., stocks extended their bull market run, with the S&P 500 Index advancing 4.40%. Investors also demonstrated a preference for growth stocks, with the Russell 3000 Growth Index returning 6.59%, versus the Russell 3000 Value Index, up 2.82%. Emerging market equities gained 4.04%, as measured by the MSCI Emerging Market Index.

Convertible securities, which combine attributes of stocks and fixed income securities, captured a substantial measure of the stock market’s gains. U.S. convertibles advanced 3.64%, as measured by the BofA Merrill Lynch All U.S. Convertibles ex-Mandatory Index, and global convertibles gained 4.11%, as measured by the BofA Merrill Lynch Global 300 Convertible Index. In the high yield bond market, the Credit Suisse High Yield Index advanced 1.33%.

These gains were earned despite headwinds related to energy prices, unrest in Ukraine, political wrangling in the euro zone, global growth rates and the potential impact of a strengthening dollar. In the U.S., unemployment continued to fall, the Federal Reserve maintained accommodative monetary policy, and corporate profits remained healthy. Outside the U.S., positive economic surprises in Europe and Japan boosted investor sentiment. Markets responded favorably to the European Central Bank’s decision to move forward with quantitative easing as well as to Japan’s concerted and coordinated efforts to promote economic recovery.

Our Use of Leverage**

We have the flexibility to utilize leverage in this Fund. Over the long term, we believe that the judicious use of leverage provides us with opportunities to enhance total return and support the Fund’s distribution rate. Leverage strategies typically entail borrowing at short-term interest rates and investing the proceeds at higher rates of return. During the reporting period, we believed the prudent use of leverage would be advantageous given the economic environment, specifically the low borrowing costs we were able to secure. Overall, use of leverage contributed favorably to the returns of the Fund, as the performance of the Fund’s holdings exceeded the cost of borrowing.

Consistent with our focus on risk management, we have employed techniques to hedge against a rise in interest rates. We have used interest rate swaps to manage the borrowing costs associated with the Fund’s use of leverage. Interest rate swaps allow us to “lock down” an interest rate we believe to be attractive.

Although rates are at historically low levels across much of the fixed income market, experience has taught us that rates can rise quickly, in some cases, in a matter of months. We believe the Fund’s use of interest rate swaps is beneficial because it provides a degree of protection should a rise in rates occur. However, we will continue to assess the costs versus benefits of employing swaps as part of our leverage strategy.

Outlook

Our team is optimistic about the global markets. Although the U.S. economy grew slowly during the first quarter of the year—due in large measure to unseasonably cold weather and turmoil in the energy sector—we believe the U.S. can resume its steady expansion for the remainder of 2015, as energy prices stabilize, inflation remains contained, and the Federal Reserve maintains its accommodative stance. We also expect the global economy to expand in 2015, benefiting from ranging factors including central bank policy in the euro zone, Japan, and select emerging markets.

While we see opportunities among equities, convertibles and high yield securities, we are concerned about the potential risks associated with oversized allocations to traditional fixed-income securities, as history has shown that interest rates can rise quickly. We believe investors should work proactively with their financial advisors to ensure appropriate diversification, which may include convertibles strategies and liquid alternative strategies.

While we see a good deal of opportunity, this is an environment where active management, rigorous research and keen awareness of risk will be important drivers of success. We anticipate market volatility will persist as investors respond to the activities of central banks (particularly those of the Federal Reserve), as well as geopolitical uncertainties. We are confident that our disciplined, tested, and fundamentally driven approach will serve the Fund well.

In closing, I invite you to visit us at www.calamos.com. We’re continually updating our site with thought leadership, blogs and commentary designed to help you and your financial advisor decide which opportunities are most appropriate for you.

On behalf of all of us at Calamos Investments, I thank you for your trust. We are honored you have chosen us to help you pursue your investment goals.

Sincerely,

John P. Calamos, Sr.

CEO and Global Co-CIO

Before investing, carefully consider a Fund’s investment objectives, risks, charges and expenses. Please see the prospectus containing this and other information or call 800.582.6959. Please read the prospectus carefully. Performance data represents past performance, which is no guarantee of future results. Current performance may be lower or higher than the performance quoted.

The MSCI World Index is a market-capitalization weighted index composed of companies representative of the market structure of developed market countries in North America, Europe and the Asia/Pacific region. The MSCI World Growth Index captures large and mid cap securities exhibiting overall growth style characteristics across 23 developed markets countries. The S&P 500 Index is an unmanaged index generally considered representative of the U.S. stock market. The Russell 3000 Growth Index measures the performance of the broad growth segment of the U.S. equity universe. It includes those Russell 3000 companies with higher price-to-book ratios and higher forecasted growth values. The Russell 3000 Value Index measures the performance of the broad value segment of the U.S. equity universe. It includes those Russell 3000 companies with lower price-to-book ratios and lower forecasted growth values. The MSCI Emerging Markets Index is a free float-adjusted market capitalization index considered broadly representative of emerging market equity performance. The index represents companies within the constituent emerging markets that are available to investors worldwide. The BofA Merrill Lynch All U.S. Convertibles Ex-Mandatory Index represents the U.S. convertible securities market excluding mandatory convertibles. The BofA ML Global 300 Convertible Index is a global convertible index composed of companies representative of the market structure of countries in North America, Europe and the Asia/Pacific region. The Credit Suisse High Yield Index is considered generally representative of the high-yield bond market. The MSCI EAFE Index measures developed market equity performance excluding the U.S. and Canada. Sources: Lipper, Inc.; Morningstar.

Unmanaged index returns assume reinvestment of any and all distributions and, unlike fund returns, do not reflect fees, expenses or sales charges. Investors cannot invest directly in an index. Investments in overseas markets pose special risks, including currency fluctuation and political risks. These risks are generally intensified for investments in emerging markets. Countries, regions, and sectors mentioned are presented to illustrate countries, regions, and sectors in which a fund may invest. Fund holdings are subject to change daily. The Fund is actively managed. The information contained herein is based on internal research derived from various sources and does not purport to be statements of all material facts relating to the securities mentioned. The information contained herein, while not guaranteed as to the accuracy or completeness, has been obtained from sources we believe to be reliable. There are certain risks involved with investing in convertible securities in addition to market risk, such as call risk, dividend risk, liquidity risk and default risk, that should be carefully considered prior to investing. This information is being provided for informational purposes only and should not be considered investment advice or an offer to buy or sell any security in the portfolio.

GLOBAL DYNAMIC INCOME FUND (CHW)

INVESTMENT TEAM DISCUSSION

Please discuss the Fund’s strategy and role within an asset allocation.

Calamos Global Dynamic Income Fund (CHW) is a global enhanced fixed-income offering that seeks to provide an attractive monthly distribution, with a secondary objective of capital appreciation. We believe it offers a diversified way to participate in the long-term potential of global markets.

In this portfolio, we are drawing upon our team’s experience in an array of asset classes. We utilize a highly flexible approach, and can invest in equities, convertible securities and high-yield securities. We also can employ alternative strategies such as covered call writing and convertible arbitrage. Through covered call writing, we seek to generate income by selling (“writing”) options on market indexes. In the convertible arbitrage strategy, we invest in convertible securities and short sell the convertibles’ underlying equities to generate income and hedge against risk.

We believe that this broad mandate enhances our ability to capitalize on market volatility, manage potential downside risks and generate more income versus traditional fixed income funds. The allocation to each asset class and strategy is dynamic, and reflects our view of the economic landscape as well as the potential of individual securities. By combining asset classes and strategies, we believe that we are well positioned to generate income and capital gains. The broader range of security types also provides us with increased opportunities to manage the risk and reward characteristics of the portfolio over full market cycles. We believe our exposure to the equity markets was beneficial to the overall performance of the Fund.

We invest in both U.S. and non-U.S. companies, with at least 40% of assets invested in non-U.S. companies. We emphasize companies with reliable debt servicing, respectable balance sheets, and sustainable prospects for growth. Regardless of a company’s country of domicile, we favor companies with geographically diversified revenue streams and global business strategies.

How did the Fund perform over the reporting period?

The Fund gained 4.68% on a net asset value (NAV) basis for the six-month period ended April 30, 2015. On a market price basis, the Fund returned 5.01%. As a comparison to the broader global fixed income and equity markets, the MSCI EAFE Index gained 7.06% and the MSCI World Index returned 5.38% during the period. The S&P 500 returned 4.40% during the period.

At the end of the reporting period, the Fund’s shares traded at an 8.33% discount to net asset value, improving from an 8.62% discount at the beginning of the period.

SINCE INCEPTION MARKET PRICE AND NAV HISTORY THROUGH 04/30/15

Performance data quoted represents past performance, which is no guarantee of future results. Current performance may be lower or higher than the performance quoted. The principal value of an investment will fluctuate so that your shares, when sold, may be worth more or less than their original cost. Returns at NAV reflect the deduction of the Fund’s management fee, debt leverage costs and all other applicable fees and expenses. You can obtain performance data current to the most recent month end by visiting www.calamos.com.

How do NAV and market price return differ?

Closed-end funds trade on exchanges, where the price of shares may be driven by factors other than the value of the underlying securities. The price of a share in the market is called market value. Market price may be influenced by factors unrelated to the performance of the fund’s holdings, such as general market sentiment or future expectation. A fund’s NAV return measures the actual return of the individual securities in the portfolio, less fund expenses. It also measures how well a manager capitalized on market opportunities. Because we believe closed-end funds are best utilized as a long-term holding within asset allocations, we believe that NAV return is the better measure of a Fund’s performance. However, when managing the Fund, we strongly consider actions and policies that we believe will optimize its overall price performance and returns based on market price.

Please discuss the Fund’s distributions during the semi-annual period.

We employ a level rate distribution policy within this Fund with the goal of providing shareholders with a consistent distribution stream. We currently distribute $0.0700 per share per month. The Fund’s annual distribution rate was 9.31% of market price as of April 30, 2015.

We believe that both the Fund’s distribution rate and level remained attractive and competitive, as low interest rates limited yield opportunities in much of the marketplace. For example, as of April 30, 2015, the dividend yield of the S&P 500 Index stocks averaged 1.99%. Yields also remained low within the U.S. government bond market, with the 10-year Treasury and the 30-year Treasury yielding 2.03% and 2.74%, respectively.

What factors influenced performance over the reporting period?

The Fund has the ability to invest in a range of strategies including convertible securities, high yield, U.S. equities, international equities, as well as convertible arbitrage. This enables us to participate in a myriad of opportunities on behalf of our shareholders. Given this flexibility, we were able to maintain our exposure to the equity markets through our convertible holdings, which allowed us to participate in the general upward trajectory of equities.

Fund asset allocations are based on total investments and may vary over time.

In the U.S. equity sleeve, our selection and overweight within financials, particularly selection in asset managers, custody banks and regional banks were positive relative to the S&P 500 Index. In addition, our selection in technology, specifically in the hardware, storage and peripherals, was beneficial. Our selection in health care, particularly biotech and pharmaceuticals, impeded performance. Our slight overweight and selection in energy, notably oil and gas exploration and production, detracted. Our absolute return in health care was positive, albeit lower than the S&P 500 Index.

In the global equity sleeve, our selection in and overweight within utilities, the multi-utilities and electric utilities, as well as selection in and underweight within financials, specifically specialized financials, all proved helpful. From a geographic perspective, our underweight in Canada and emerging Asia served us well. Our overweight and selection within consumer discretionary, particularly automobile manufacturers, Internet retail, auto parts and equipment and cable and satellite, impeded performance. In addition, our selection and overweight in energy, especially oil and gas exploration, oil and gas equipment and services, also held back returns. Geographically, our overweight in the U.S. and underweight in Japan was not helpful.

In the international sleeve, our selection in and underweight in information technology, particularly home entertainment software, consulting and semiconductors were helpful. In addition, our selection and underweight in financials (diversified banks, asset managers and custody banks) were relatively positive. Geographically, our selection in Europe and South Africa benefitted performance. Conversely, our selections and underweight in health care (pharmaceuticals) and selection within consumer staples (brewers) underperformed relative to the Index. Geographically, our overweight in Latin America and Canada impeded relative performance.

The convertible arbitrage strategy benefited from rising equity prices as more value was gained on the long convertible than was lost on the short equity position over the six-month period. Two detractors for convertible arbitrage during the reporting period included the near-zero fed funds rate (no overnight interest received on cash from short equity positions) and widened credit spreads that exceeded the benefit from declining interest rates. The average high yield credit spread rose 34 basis points, or 0.34%, while the 5-Year Treasury yield fell 19 basis points.

How is the Fund positioned?

We believe large multinational companies with globally diversified revenues and access to capital are poised to capitalize on both secular and cyclical trends. In our estimation, valuations of global equities are selectively attractive, as investors continue to discount the growth of future cash flows. Equity and equity-sensitive securities continue to offer attractive risk-reward characteristics from a long-term perspective. We continue to pursue our strategic objective of participating in a significant portion of equity market upside while aiming to reduce volatility versus global equities over a complete market cycle.

The portfolio’s largest allocations, in absolute terms, are to the information technology, financials and consumer discretionary sectors. We believe that many information technology companies offer compelling fundamentals as well as participation in secular growth trends. We think that financial companies will do well in a rising-interest-rate environment. In regard to consumer discretionary, we believe that companies within the sector will be lifted by improving economic conditions.

The Fund includes a blend of high-yield and investment-grade credits. We have taken a very selective approach to CCC-rated credits, currently less than 3% of the portfolio. Given our expectation that economic growth may feel stop-and-go, we believe it is particularly important to favor companies that offer the best prospects for reliable debt servicing.

The Fund was leveraged at 28% of total assets as of the end of the period, which we believe is a moderate amount. We currently borrow through floating rate bank debt and, given low borrowing rates, this has been beneficial to the performance of the Fund. In addition, we hedge some of our floating rate debt with interest rate swaps. This is a defensive strategy that mitigates the Fund’s overall exposure to a quick rise in short-term interest rates.

Do you have any closing thoughts for Fund shareholders?

We expect global equities to deliver additional gains in 2015 but we believe investors should anticipate periods of higher volatility as markets confront sluggish global growth, policy uncertainty, and fluctuations in currencies and commodities. We believe merger and acquisition and share buyback activity may provide a floor for market valuations, and support higher prices and investor demand for equities and equity-sensitive securities. Markets will continue to confront uncertainty as commodity prices fluctuate and geopolitical events and global growth fears linger.

Convertible securities have tended to perform well in a slow-growth environment, when stocks are rising and interest rates are increasing slowly. Convertibles can also benefit from market volatility, as their embedded option can become more valuable. Because convertibles combine equity and fixed income characteristics, they offer the opportunity for upside equity participation with potential downside protection when equity markets decline. Against this backdrop, we believe the benefits of convertible securities are especially pronounced.