本文的目的在於探討蜜月期選舉時程如何在半總統制下，對前三大政黨在國會選舉時的表現，產生不同於在總統制下所產生的影響。本文認為，由於總統制與半總統制的權力分立程度不同，所以導引出來的蜜月期選舉效應也就相異。根據既有文獻可知，在總統制下，因為權力完全分立，總統黨與第三黨在以具有比例性的選制所進行的蜜月期國會大選中會選得比較好，但本文認為這個效應無法類推到半總統制國家。在半總統制下，因為權力只有部分分立，國會大選是行政權選舉的第二階段，所以即便在蜜月期選舉時程中，前兩大黨仍會選得比第三黨好，而和總統制國家的經驗不同。本研究分析半總統制民主國家的蜜月期選舉資料，並且針對各國的共治經驗以及臺灣的個案進行較為深入的探討，結果支持了本文的論點:相對於第二大黨，半總統制國家的第三大黨並不會因為蜜月期選舉時程，而選得比較好。文章最後也將簡短討論小黨在其他選舉時程下的可能發展。

This paper aims at exploring how semi-presidentialism differs from presidentialism in affecting electoral performance of three largest parties in honeymoon elections. This paper argues that different levels of power separation in presidentialism and semi-presidentialism explain why the effects of honeymoon elections vary. Many existent studies indicated that in presidential systems, with total power separation, the largest and the third largest parties would gain in honeymoon elections that used proportional electoral systems. The combined effect of honeymoon elections and proportional electoral systems does not exist in semi-presidential systems, however. In semi-presidentialism, there is only partial power separation, and parliamentary elections are generally second stages of executive elections. Therefore, in semi-presidentialism, honeymoon elections using proportional electoral systems tend to benefit the largest and the second largest parties. This study analyzes data from six honeymoon elections of four semi- presidential democracies, and discusses the cohabitation experiences of these countries. Empirical findings support the hypothesis of this paper. Possible effects of other electoral cycles on small parties’ electoral performance are also briefly discussed.