This study aimed to identify the principle of separation of powers and shed light on the formation and competencies of the three branches of government in contemporary political systems, particularly the presidential and semi-presidential systems, through a comparison between the Turkish presidential system and the French semi-presidential system. To achieve the objectives of the study, the comparative method and the descriptive-analytical method were relied upon. The study concluded several findings, including that the optimal application of the principle of separation of powers in contemporary political systems necessarily leads to the realization of the desired democracy among all peoples of the world. The study showed the existence of similarities in the application of the principle of separation of powers between the Turkish and French systems, particularly in the formation of the executive and judicial branches, and the powers of the legislative and judicial branches in both systems. The study showed that the Turkish presidential system has achieved comprehensive democracy through the optimal application of the principle of separation of powers, unlike the French semi-presidential system, which has lost its constitutional and comprehensive democratic nature. This is reflected in the formation of the French legislative branch, which was not fully constituted through popular elections. Instead, this branch is divided into two parts: the National Assembly, which is formed through direct popular elections, and the Senate, which is formed through elections for a specific category, including senators, members of the councils of French expatriates, and municipal council representatives, without a general popular vote, contrary to the principle of separation of powers. The study also highlighted the encroachment of the executive branch on the judicial branch in the French semi-presidential system, by granting the French president the power to issue pardons in certain cases where judicial rulings had already been made by the judiciary, contrary to the optimal application of the principle of separation of powers, which requires functional separation between the executive and judicial branches. Finally, the Turkish presidential system is more democratic due to the optimal application of the principle of separation of powers, compared to the French semipresidential system.