The KOSPI closed at 6,627.26 on September 15, down 57.11 points, or 0.85%, as rising U.S. Treasury yields, elevated oil prices and continued concerns about an AI slowdown weighed on the market. The index opened lower, moved around the flatline and then weakened as macroeconomic conditions deteriorated, finishing near 6,600. The U.S. 10-year Treasury yield reached 5.026%, its highest level since October 2023, according to Bloomberg News. November Brent crude futures settled at $105.68 per barrel on September 14 local time, while October West Texas Intermediate crude futures stood at $101.39. Those conditions strengthened expectations for a Federal Reserve rate increase on September 16 local time, with the CME FedWatch Tool putting the probability of a 0.25 percentage-point hike at 92.4%. Foreign investors and institutions sold a net 1.5711 trillion Korean won and 903.9 billion Korean won, respectively, while individuals and other corporations bought a net 831.9 billion Korean won and 1.6431 trillion Korean won, cushioning the decline. Samsung Electronics and SK Hynix edged higher, Samsung Electronics Preferred Shares gained 2% after Life Asset Management proposed a buyback and cancellation, and secondary battery stocks including LG Energy Solution benefited from U.S.-related momentum against China. The KOSDAQ rose 0.7% to 812.41, supported by net buying from foreign investors and institutions, while humanoid robot shares such as SPG gained after Goldman Sachs forecast 6.5 million global humanoid robot shipments by 2035. EcoPro also strengthened, whereas semiconductor materials, parts and equipment shares including Jusung Engineering fell.