As of 0157 GMT, the main TAIEX index fell 77.51 points to 8,690.88, trailing other regional and global bourses, after closing up 0.65 percent on Tuesday.
For the month to date, foreign investors have been net sellers in the Taiwan market in every session except one, putting heavy pressure on equities.
The electronics subindex fell 0.78 percent, dragged down by key Apple Inc suppliers Hon Hai Precision Industry Co Ltd, which fell 3.23 percent, Pegatron Corp, down 2.2 percent, and case maker Catcher Technology Co Ltd, off 4.8 percent.
Banks and insurance holdings shed 1 percent, while autos suffered a 1.1 percent tumble.
The Taiwan dollar was up T$0.021 to stand at T$30.408 to the US dollar.