台灣加權指數期貨每日平均交易量可達十萬以上，其中又以近月台指加權指數期貨合約最為熱門，市場上的報價也會以近月合約價格為主。但受限於期貨合約特性，該月份到期的期貨合約在最後交易日後，需要進行換約。在過去八年，台灣加權指數成分股多半集中於6~8月份進行除息，而此時換月的期貨契約因而容易產生換月價差。我們認為期貨會提前反應各成分股的除息點數。本論文研究主要透過換月價差及期貨基差，探究期貨合約是否在6~8月份較易因換約而造成價格下降的現象，並且透過期貨基差收斂特性，設計投資策略進行回測研究。
利用過去八年的台指期價格歷史資料，我們發現期貨換月價差容易在6~8月份發生，尤其在期貨契約換約後的第一天，期貨報價較前一天下降許多。透過基差分析我們發現，相較於其他月份，在6~8月份換月後的基差相對其他月份低，顯示期貨價格會提前反應台指成分股公司除息現象。

Due to the feature of futures contracts, a futures contract approaching to maturity needs to be roll-overed to the next near futures contract after the last trading date of the maturity month. The price spread of the two futures would occur during the rollover period. In Taiwan, most companies go ex-dividend in the period of June to August. The purpose of this research is to examine whether the price spread of the last trading date for a TAIEX futures contract in the period of June to August will be significantly different from that in other periods.
Our sample from 2011 to 2018 show that more than eighty percent of companies would go ex-dividend from June to August. The empirical analysis shows that the price spread in the last trading date of June to August is significantly different from that of other maturity months. Moreover, the basis of futures contracts during the June to August period would be lower than that of other months. Based on these findings, we propose a trading rule trying to optimize the reward-risk ratio of an investment strategy.

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