本研究旨在探討公司治理對併購溢酬及主併公司併購後經營績效之影響，以「治理指數」整合性指標為基礎，擴展研究設計。為更全面呈現公司治理之效果，進一步納入外部獨立董事、最大外部股東及法人持股等外部治理監督機制，從內外部治理機制互動的觀點，分析其對併購成效之影響及可能存在之關聯。
本研究以2005年至2019年間台灣企業併購事件為研究樣本，採用實證方法進行分析。實證結果顯示，併購溢酬與內、外部公司治理機制之間未呈現顯著關聯。就併購後經營績效而言，最大外部股東持股比例與每股盈餘（EPS）、股東權益報酬率（ROE）及總資產報酬率（ROA）呈現正向且顯著之關係；法人持股比例則與ROA及Tobin’s Q呈現顯著負向關聯。外部獨立董事在六年觀察期間僅於單一年度對Tobin’s Q產生正向且顯著之影響，而內部治理指數與併購後績效則無顯著關聯。
整體而言，外部治理機制對併購後經營績效具有限度之影響，而內部治理機制之效果則不顯著。研究結果可作為企業在公司治理制度建置與調整，以及外部政策修訂時之參考，並為投資人提供實務上之投資決策依據。

This study investigates the impact of corporate governance on merger premiums and the subsequent operating performance of the acquiring company using the "Governance Index" as a key indicator. Additionally, it incorporates external governance mechanisms, including independent directors, the largest external shareholders, and institutional holdings, to assess the external monitoring of corporate governance. The study explores the interplay between internal and external governance systems in the context of mergers and acquisitions.
Empirical methods are used to evaluate Taiwanese firm mergers and acquisitions from 2005 to 2019. The results indicate no significant correlation between merger premiums and either internal or external governance mechanisms. The proportion of shares owned by the largest external shareholder exhibits a significant positive correlation with return on equity (ROE), earnings per share (EPS), and return on assets (ROA) regarding post-merger operating performance. In contrast, institutional ownership is significantly negatively correlated with both ROA and Tobin's Q. The internal governance index showed no significant correlation with post-merger performance over the six-year observation period, while external independent directors positively and significantly influenced Tobin's Q in only one year.
In conclusion, the findings suggest that external governance systems have a limited effect on post-merger performance, whereas the influence of internal governance mechanisms is negligible. This study provides valuable insights for businesses in shaping and adjusting their corporate governance structures, revising external regulations, and offering practical investment guidance for investors.

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