The KOSPI snapped a four-session losing streak with a 1.37% jump to 6,717.97, while the won slid roughly 1.6% to around 1,368 per dollar as of the Seoul close — an unusual split, with the Fed’s September decision still hours away.
The KOSPI fell 0.85% as foreign and institutional investors sold over 2 trillion won amid $101 oil, 5% US yields and AI-pacing worries, while the KOSDAQ rose 0.70% on a cybersecurity stock surge. The won weakened to 1,359.68 per dollar ahead of the FOMC.
Rising US 10-year Treasury yields hit Korean stocks through three channels: a higher global discount rate that compresses Samsung and SK Hynix valuations, a wider US-Korea rate gap that lifts USD/KRW, and foreign selling on the KRX. Here is how each channel works, which thresholds matter, and how to read the daily foreign-flow print step by step.
The KOSPI fell 3.26% to 6,684.37 as foreign investors and institutions sold roughly $3 billion of stock ahead of the September 17 FOMC. Chip giants led the losses while cybersecurity and optical-networking small caps surged against the tide.
The KOSPI fell 1.76% to 6,909.91 after an early 3% plunge, as WTI topped $100 on US-Iran escalation and US yields spiked. Foreigners and institutions sold over $3 billion; retail bought the dip. All eyes now turn to tonight’s US CPI.
Korea allows only covered short selling, enforces an uptick rule, and has banned shorting outright after every major crisis since 2008. Here is how the regime works, why retail access is contested, and how to read flow data like the KRW 2.6 trillion foreign outflow of 2026-09-10.
KOSPI slipped 0.25% to 7,033.92 after a 174-point intraday swing on quadruple witching day, as foreigners sold a net $1.9 billion. KOSDAQ rose 0.79% on heavy institutional buying, and Brent’s break above $100 redrew the sector map.
The KOSPI closed above 7,000 for the first time in about two months, up 1.40%, as OpenAI’s GPT-6 launch lifted chip sentiment and battery materials rallied. Individuals sold a hefty 2.5 trillion won while institutions bought.
Seoul’s KOSPI surged past 7,000 intraday on AI memory-demand hopes tied to OpenAI’s upcoming ‘Astra’ model, then closed down 0.58% at 6,954.52 as retail investors dumped over 3 trillion won of stock. Oil and a US-Canada trade fight added pressure.
A move in USD/KRW from about 1,345 to 1,450 erases roughly 7% of a dollar-based KOSPI return before a single stock price moves. This guide explains the FX feedback loop, why the 1,400-1,500 zone matters, hedged vs unhedged exposure, and how to read foreign flow data in eok won.