半總統制兼具總統制與議會內閣制的特徵，在運作上也存在往總 統制或往議會內閣制偏移，甚至轉型的可能。在實際的經驗上，有些國家維持了半總統制的制度框架，實質運作依照議會內閣制的憲政秩序；有些國家則是經過修憲，徹底將制度規範調整爲議會內閣制。以 實際個案的分佈來說，議會化的半總統制以歐洲地區民主運作穩固的國家居多，例如奧地利、芬蘭、冰島、愛爾蘭等。而後共地區的半總 統制國家，則大多呈現總統化、或是總統與總理競爭、甚至高度不穩定的狀態。雖然如此，仍有少數的後共國家在過去幾年來的憲政運作逐漸趨於穩定，並且往議會制傾斜。其中，保加利亞就是一個持續往 議會制傾斜的顯著個案。半總統制在後共國家出現了系統性的發展歷程，和民主轉型後的政黨體系發展、總統權力的擴張或限縮有關。本文認爲，總統權力的設計、政黨體系的發展、以及總統-總理的黨政 關係，是影響半總統制往總統或是往議會偏移或深化的關鍵，本文以保加利亞爲分析個案，討論議會化的半總統制日益穩定的原因，就是建立在總統實質權力限縮，政黨體系穩定，以及以總理爲黨政關係樞紐的基礎之上。

Semi-presidentialism is a miXed form with the essences of parliamentary and presidential systems. The constitutional operation of semi-presidentialism thus may be similar to parliamentary (parliamentarized semi-presidentialism) or presidential (presidentialized semi-presidentialism) systems. Generally speaking, “parliamentarized semi-presidential” countries are mostly found in Europe, including Austria, Finland, Iceland, and Ireland. In addition, many post-communist countries are tending toward presidentialized semi-presidentialism or are unstable because of the keen competition between president and prime minister. But there are still a few post-communist countries in which the constitutional operation is tending toward a parliamentary system. Bulgaria is one eXample. Under semi-presidentialism, factors that affect constitutional operation include party politics and the president’s constitutional power. This paper eXamines constitutional operation in relation to party politics, the president’s power, and the relationship between president and prime minister. Bulgaria is developing into a parliamentarized semi-presidential system on the basis of a stable party politics, a president with limited power, and the prime minister as the party leader.