Taiwan's TAIEX fell, led by exporters such as Asustek Computer Inc (華碩電腦), after a US government report showed economic growth slowed more than expected in the second quarter.
Formosa Plastics Corp (台塑) gained after a local newspaper said the nation's plastics makers raised prices for August as supply declined.
The TAIEX dropped 23.79, or 0.5 percent, to 4916.59, as more than three stocks fell for every two that rose. The total value of trade was NT$53.89 billion (US$1.6 billion), more than a fifth below the three-month daily average.
The US economy grew at a 1.1 percent annual rate in the three months to June 30, less than the 2.3 percent increase expected by economists. The US is the second-largest buyer of Taiwan's semiconductors.
Asustek, which makes computer boards for customers such as Dell Computer Corp and Hewlett-Packard Co, dropped NT$6, or 6.4 percent, to NT$87.50.
"The computer motherboard makers are saying August orders aren't that strong," said Brian Huang, who helps manage NT$3 billion (US$89 million) in stocks at Truswell Securities Investment Trust Co (富鼎投信). "Investors are moving funds from electronics stocks to traditional-industry stocks."
Formosa Plastics, Taiwan's second-largest plastics-maker, rose NT$1.10, 2.5 percent, to NT$45.80. Chemicals and plastics makers raised prices for August after rivals in Japan and Korea halted production for maintenance.
China Motor Co (中華汽車) added 10 cents, or 0.2 percent, to NT$45.10. Sales in July rose almost two-fifths from a year earlier to NT$4.98 billion as the automaker sold more of its Lancer and Savrin models.
Evergreen Marine Corp (長榮海運) dropped 70 cents, or 4.4 percent, to NT$15.30. The company said June sales fell more than a quarter to NT$1.1 billion. Sales in the first half shed more than a fifth to NT$6.9 billion.
High Tech Computer Corp (宏達電腦) rose NT$1, or 0.8 percent, to NT$126.50 after media reports that the company will supply hand-held organizers to AT&T Corp and Microsoft Corp. High Tech wouldn't comment.
Ambit Microsystems Corp (國電) fell 50 cents, or 0.6 percent, to NT$90.50. The maker of modems and power units for customers such as Apple Computer Inc reported first-half profit of NT$910 million, reaching 45 percent of its target for the year.
Taiwan Green Point Enterprises Co (台灣綠點) fell NT$2.50, or 3.9 percent, to NT$62. The maker of mobile-phone plastic molds for customers such as Motorola Inc said first-half pre-tax profit of NT$191.5 million reached 32 percent of its full year target.
Chien Tai Cement Co (建台水泥) fell 10 cents, 4.9 percent, to NT$1.93.