As of 0140 GMT, the main TAIEX index had fallen to 8,535.58, extending its 1.3 percent loss in the previous session.
The electronics sub-index slipped 1.3 percent, with the world's top contract chipmaker TSMC and Apple Inc supplier Largan Precision both down about 1 percent.
TSMC and Largan are set to report their latest quarterly numbers after market hours.
Foreign investors have sold a net T$33 billion ($1.1 billion) so far this month.
Banking and food stocks lost 1 percent and 2 percent, respectively.
The Taiwan dollar was up 0.217 percent at T$30.354 to the US dollar.