在本文中，我們主要探討1990年1月到2007年12月美國上市公司，其可轉債持有者是否會因公司本身的公司治理程度優劣，而影響可轉債的轉換策略，我們利用反購併條款建立的公司治理指數(G-index)來衡量公司外部治理程度，探討公司治理政策與投資人的可轉債轉換機率之間的關係。本文第一個假說預期，當標的公司的治理程度越佳時，可轉債持有者在到期日前傾向執行選擇權而將可轉債轉換成股票的機率越高，使得可轉債的特性較偏向權益證券(equity-like)。第二個假說則認為，當公司內部持股結構改變時，法人持股比例會是影響公司治理以及轉換機率關係的重要因子之一。實證結果指出，當公司治理指數越高時，表示管理階層的控制程度越強，可轉債投資人持有的預期轉換機率也會顯著較低；若考慮進法人持股比例，則兩者的反向關係會更加強烈，證實公司本身的股權結構也會間接影響可轉債投資者的轉換策略。另一方面，本研究在穩健性測試中使用預期轉換期間來表示投資人轉換策略，實證結果發現，公司治理指數低的公司表示股東保護權利較佳，其投資人將會有提前轉換的可能性存在，兩者存在正向關係，此與前者的分析具一致性的結論，由此證明可轉債發行時的公司治理程度，會是可轉債投資人考量的重要因素之一。

In this article, we examine the convertible issues in U.S. market from January 1990 to December 2007, to investigate the conversion probability of issues with different G-index, which is a widely-used index for evaluating a firm’s equity holders’ right as well as corporate governance. In contrast to prior researches, we try to understand how a firm’s corporate governance affects convertible bondholders’ converting behavior. First, we hypothesize that for firms with better corporate governance, convertible bondholders are more willing to become shareholders by exercising the option to convert the debt into equity, and the convertible bond is therefore more equity-like. In the second hypothesis, we expect that the percentage of non-manager institutional shareholdings would strengthen the association between expected conversion probability and corporate governance. The empirical results show that higher G-index which implies stronger managerial control significantly lead to lower expected conversion probability. Besides, the ownership structure also affects the association. In robustness check, we alternatively define expected time to conversion. Similarly, for firms with better corporate governance, the convertible bondholders would convert debt into equity shortly. As a whole, the expected time to conversion is negatively related to the expected conversion probability at the maturity. Therefore, the convertible bondholders will take the level of managerial control into consideration to exercise their conversion option.

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