An electronic board showing the Korea Composite Stock Price Index at a dealing room of the Hana Bank headquarters in Seoul on Thursday. (Yonhap) Seoul stocks opened sharply lower Thursday as a sell-off of US semiconductor shares weighed on market sentiment, while investors assessed fresh remarks from Federal Reserve Chairman Kevin Warsh.After opening 4.46 percent lower, the benchmark Korea Composite Stock Price Index extended losses, plunging 517.25 points, or 6.23 percent, to 7,790.16, as of 9:15 a.m.Due to the sharp drop, the bourse operator Korea Exchange activated a sell-side sidecar for the Kospi around 9:07 a.m., halting program trading for five minutes.A sell-side sidecar is triggered when the Kospi 200 Futures index decreases 5 percent or more for at least one minute.US stocks retreated overnight. The S&P 500 slipped 0.2 percent, while the tech-heavy Nasdaq 100 fell 1.5 percent. The Philadelphia Semiconductor Index, a key gauge of chip stocks, tumbled 6.3 percent.Fed Chair Warsh said inflation expectations and inflation risks have eased in recent weeks, dampening hopes for a July interest rate cut.Investors also remained cautious over the latest developments in US-Iran talks after the two sides concluded another round of indirect negotiations on Wednesday without any clear signs of progress toward lasting peace.Market heavyweights were down across the board.Top market cap Samsung Electronics tumbled 7.47 percent, and chip giant SK hynix plunged 7.73 percent.AI investment firm SK Square sank 10.23 percent, and top automaker Hyundai Motor shed 5.33 percent.The Korean won was trading at 1,554.3 won against the US dollar, up 0.6 won from the previous session. (Yonhap)