Why did the KOSPI fall 5.8 percent on Thursday?

Investor sentiment was weakened by concerns that massive AI investments may not generate expected returns and by hotter-than-expected U.S. inflation. Overnight losses on Wall Street, including declines in the S&P 500 and Nasdaq, added to the pressure on Seoul shares.

How did major Korean companies and the won perform during the sell-off?

Samsung Electronics fell more than 6 percent and SK hynix dropped more than 8 percent. Hyundai Motor declined 4.31 percent, while Hanwha Aerospace and Celltrion fell 0.24 percent and 1.39 percent, respectively; the won traded at 1,343.3 per dollar.

Seoul stocks open sharply lower on lingering concerns over AI, US inflation

Q: What triggered the sell-side sidecar in Seoul trading?

The KOSPI’s sharp early-morning decline triggered the bourse operator to issue a sell-side sidecar soon after the market opened. The index had fallen 348.47 points, or 5.8 percent, to 5,660.34 by 9:15 a.m.

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Summary

The KOSPI tumbled 348.47 points, or 5.8 percent, to 5,660.34 in Seoul on Thursday as of 9:15 a.m., amid concerns about AI investment returns and hotter-than-expected U.S. inflation. The decline triggered a sell-side sidecar and extended Seoul stocks’ losing streak to six sessions. Samsung Electronics and SK hynix fell more than 6 percent and 8 percent, respectively, while the won weakened to 1,343.3 per dollar.

Key Facts

The U.S. Consumer Price Index rose 0.6 percent in September from the previous month, bringing annual inflation to 3.7 percent versus economists’ 3.6 percent expectation.
The S&P 500 fell 1.11 percent and the Nasdaq declined 1.88 percent overnight.
Hyundai Motor dropped 4.31 percent, Hanwha Aerospace slipped 0.24 percent and Celltrion retreated 1.39 percent.
The Korean won weakened by 1 won from the previous session’s close to trade at 1,343.3 won per U.S. dollar as of 9:15 a.m.

By Yonhap

Published Oct 15, 2026 9:16 am KST
Updated Oct 15, 2026 9:36 am KST

The benchmark KOSPI is displayed at a dealing room of Hana Bank in Seoul, Thursday. Yonhap

Seoul stocks opened sharply lower Thursday, as concerns over the sustainability of artificial intelligence (AI) and hotter-than-expected inflation in the United States dampened investor sentiment.

After opening sharply lower, the benchmark Korea Composite Stock Price Index (KOSPI) tumbled 348.47 points, or 5.8 percent, to 5,660.34 as of 9:15 a.m.

The sharp drop in the index triggered the country's bourse operator to issue a sell-side sidecar soon after the market opened.

Seoul stocks have continued their losing streak for the past six consecutive sessions.

Major stock indexes on Wall Street closed lower overnight amid growing inflation concerns and skepticism over whether the AI boom could live up to investors' expectations.

The S&P 500 shed 1.11 percent, and the tech heavy Nasdaq dipped 1.88 percent.

The U.S. Consumer Price Index rose 0.6 percent in September from a month earlier, bringing the annual rate of inflation to 3.7 percent, above economics' expectations for a 3.6 percent increase.

Also, investors still remained skeptical about whether AI investment could generate expected returns.

Seoul's two chip giants moved in tandem with tech firms on Wall Street, with Samsung Electronics and SK hynix dipping over 6 percent and 8 percent, respectively.

Carmaker Hyundai Motor shed 4.31 percent, defense giant Hanwha Aerospace inched down 0.24 percent, and bio firm Celltrion retreated 1.39 percent.

The Korean won was trading at 1,343.3 won against the U.S. dollar as of 9:15 a.m., down 1 won from the close of the previous stock trading session.

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