This paper investigates the effect of internal corporate governance mechanisms and control variables, such as bank size and bank age on bank financial performance. The sample of this study comprises of both conventional and Islamic banks operating in the seven Arabian Peninsula countries, namely Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, United Arab Emirates, and Yemen. Regression analysis (OLS) is used to test the effect of corporate governance mechanisms on bank financial performance. The results of this study reveal that there is a significant relationship between corporate governance and bank profitability. Board size, board activism, number of outside directors, and bank age significantly affect Tobin's Q. Meanwhile, ROA and PM are affected by ownership concentration, audit committee, audit committee meetings, and the age & size of the bank. The results are consistent with previous literature that the correlation between corporate governance and firm performance is still not clearly established and that impact of corporate governance on bank financial performance in developing countries is still relatively limited.