An electronic board showing the Korea Composite Stock Price Index at a dealing room of the Hana Bank headquarters in Seoul on Wednesday. (Yonhap) Seoul shares plunged by nearly 6 percent Wednesday following a nearly 11 percent crash the previous session as investors dumped semiconductor stocks amid growing skepticism over whether massive spending on artificial intelligence will generate sufficient returns.The local currency strengthened against the US dollar.The benchmark Korea Composite Stock Price Index lost 360.42 points, or 5.98 percent, to close at 5,663.24, after plunging to an intraday low of 5,262.77.After opening 1.09 percent higher, the KOSPI reversed course and tumbled by up to nearly 12 percent in afternoon trading.At 12:31 p.m., the Korea Exchange activated a marketwide circuit breaker, halting trading in KOSPI-listed stocks for 20 minutes.The broad-based sell-off came amid growing skepticism over whether hefty AI-related investments by major technology companies could generate sufficient returns to justify their lofty market valuations."Rising competition from China following the successful listing of ChangXin Memory Technologies also weighed on investor sentiment," Na Jeong-hwan, an analyst at NH Investment & Securities Co., said.Trade volume was high at 449.29 million shares worth 47.83 trillion won ($33 billion), with losers sharply outnumbering winners 804 to 91.Foreigners and individuals offloaded a net 1.23 trillion won and 1.97 trillion won worth of stocks, respectively. Institutions purchased a net 3.16 trillion won.In Seoul, tech stocks led the decline.Market bellwether Samsung Electronics fell 5.23 percent to 208,500 won, and SK hynix plunged 9.61 percent to 1.4 million won.Top carmaker Hyundai Motor tumbled 2.88 percent to 353,500 won, and its sister Kia sank 1.15 percent to 120,400 won.Internet giant Naver slid 4.05 percent to 201,500 won, and energy firm Doosan Enerbility dipped 6.03 percent to 60,800 won.Among gainers, shipping firm HMM rose 1.25 percent to 20,250 won and No. 1 auto parts maker Hyundai Mobis climbed 1.14 percent to 445,000 won.The Korean won was quoted at 1,446.7 won against the US dollar as of 3:30 p.m. compared with 1,462.5 won a day earlier.Bond prices, which move inversely to yields, closed higher. The yield on three-year Treasurys fell 2.9 basis points to 3.800 percent, while the return on the benchmark five-year government bonds dropped 3.1 basis points to 4.037 percent. (Yonhap)