Sistem separa-presiden atau sistem dwi eksekutif adalah satu sistem kerajaan di mana Presiden wujud bersama Perdana Menteri berserta sebuah kabinet, dengan PM bertanggungjawab pada badan perundangan negara. Ia berbeza dari republik berparlimen kerana ia mempunyai ketua negara yang dipilih secara umum, yang lebih merupakan pemimpin simbolik beristiadat, dan dari sistem berpresiden didalam kabinet tersebut, walaupun dinamakan oleh presiden, adalah bertanggungjawab pada badan perundangan, yang mungkin memaksa kabinet untuk meletakkan jawatan melalui undi tidak percaya.[1][2][3][4]
Walaupun Republik Weimar (1919–1933) mencontohkan sistem separa-presiden yang terawal, istilah "separa-presiden" telah diperkenalkan dalam artikel 1959 oleh wartawan Hubert Beuve-Méry[5] dan dipopularkan dari karya 1978 oleh saintis politik Maurice Duverger,[6] kedua-duanya bertujuan untuk menggambarkan Republik Kelima Perancis (ditubuhkan pada tahun 1958).[1][2][3][4]
The concept of a semi-presidential form of government, as used here, is defined only by the content of the constitution. A political regime is considered as semi-presidential if the constitution which established it, combines three elements: (1) the president of the republic is elected by universal suffrage, (2) he possesses quite considerable powers; (3) he has opposite him, however, a prime minister and ministers who possess executive and governmental power and can stay in office only if the parliament does not show its opposition to them.CS1 maint: ref=harv (link)
The conventional analysis of government in democratic countries by political science and constitutional law starts from the traditional types of presidentialism and parliamentarism. There is, however, a general consensus that governments in the various countries work quite differently. This is why some authors have inserted distinctive features into their analytical approaches, at the same time maintaining the general dichotomy. Maurice Duverger, trying to explain the French Fifth Republic, found that this dichotomy was not adequate for this purpose. He therefore resorted to the concept of 'semi-presidential government': The characteristics of the concept are (Duverger 1974: 122, 1978: 28, 1980: 166):CS1 maint: ref=harv (link)
1. the President of the Republic is elected by universal suffrage,
2. he possesses quite considerable powers and
3. he has opposite him a prime minister who possesses executive and governmental powers and can stay in office only if parliament does not express its opposition to him.