Taiwan (the Republic of China, ROC) adopted a semi-presidential system in the 1997 constitutional reform. That system is now being put to the test through the transfer of power from the Kuomintang (KMT) to the Democratic Progressive Party (DPP) given that the DPP won the 2000 presidential elections. This paper first develops a theoretical framework to analyze political stability under different types of semi-presidential systems. Three factors are singled out as the most critical: presidential power (high or low), president-parliament relations (congruent or incongruent),and party system (biparty or multiparty). Following is a look into Taiwan's institutional background and its process of constitutional reform. We discover that after the inauguration of President Chen Shui-bian, Taiwan fell into a highly unfavorable situation, with a low stability rating. The second part of the paper focuses on the interaction mode between the president and the parliament which is characterized by incongruent relations. Four empirical cases are used to demonstrate the four interaction modes under incongruence: the French Fifth Republic ("cohabitation"), Finland ("division of labor"), Weimar Germany ("collision"), and the Russian Federation ("supremacy of the president"). The Chen (Shui-bian)-Tang (Fei) duarchy is closer to the Finnish "division of labor" system than to any other interaction mode, but with less presidential concessions. This setup is clearly a compromise rather than cohabitation. As such, the Chen-Tang system is useful in defusing parliamentary opposition in the short term, but is conflict-prone in nature, as born out by its ultimate collapse.