अर्ध-अध्यक्षीय प्रणाली अथवा अर्ध राष्ट्रपति प्रणाली, शासन की वह प्रणाली होती है, जिसमें राज्य के कार्यकारी अधिकार पूर्णतः एक कार्यकारी राष्ट्राध्यक्ष के अंतर्गत ना हो, बल्कि कुछ कार्यकारी शक्तियां अन्य अधिकारीयों व संस्थाओं के अंतर्गत हों, जो स्वतंत्र रूप से कार्य कर सकें। यह किसी अध्यक्षीय प्रणाली से भिन्न है, जिसमें सम्पूर्ण कार्यकारी शक्तियन एक ही अधिकारी (राष्ट्राध्यक्ष या शासनाध्यक्ष) के अंतर्गत आती हैं।
इस शासन प्रणाली में एक कार्यकारी राष्ट्रपति एक प्रधानमंत्री और कैबिनेट के साथ मौजूद होता है, जिसमें केवल प्रधानमंत्री राष्ट्रिय विधायिका के प्रति जिम्मेदार होता है। यह संसदीय प्रणाली से भिन्न है जिसमें एक लोकप्रिय निर्वाचित शासनप्रमुख होता है, जबकि राष्ट्रप्रमुख के पास नाममात्र अधिकार होते हैं। वहीं राष्ट्रपति प्रणाली से भी यह भिन्न है जिसमें राष्ट्रपति द्वारा नामित कैबिनेट विधायिका के लिए जिम्मेदार होती है, जो अविश्वास प्रस्ताव के माध्यम से इस्तीफा देने के लिए कैबिनेट को मजबूर कर सकता है।[1][2][3][4]
Duverger (1980). "A New Political System Model: Semi-Presidential Government". European Journal of Political Research (quarterly). 8 (2): 165–187. डीओआइ:10.1111/j.1475-6765.1980.tb00569.x. 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.
Bahro, Horst; Bayerlein, Bernhard H.; Veser, Ernst (October 1998). "Duverger's concept: Semi-presidential government revisited". European Journal of Political Research (quarterly). 34 (2): 201–224. डीओआइ:10.1111/1475-6765.00405. 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): 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.
