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 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.
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.
FOMC decisions land at 3 AM KST (4 AM in US winter), and Seoul is among the first major cash markets to open on the result. Here is how to read Fed funds futures probabilities like a ‘66% priced in’ figure, what the dot plot actually commits the Fed to (nothing), and the three channels — USD/KRW, foreign flows, and the BOK rate gap — that carry the shock into the 9 AM Korean open.
US CPI hits at 21:30-22:30 KST, roughly eleven hours before the KOSPI opens. Three channels carry the surprise into Seoul’s 9:00 a.m. session: US index futures and the SOX, the USD/KRW rate, and foreign investor flow direction. Here is how to read each one, with a worked example of reading a multi-session foreign-flow tape from August 2026.
The KOSPI plunged as much as 4.3% on overnight US chip weakness before Samsung Electronics and SK Hynix powered an afternoon reversal, closing up 0.68% at 6,742.74. Foreign investors sold heavily into the dip while retail bought. Nvidia’s earnings loom Wednesday.
In Korea, a buyback lowers the share count for EPS purposes the moment the repurchased shares become treasury stock — but only cancellation makes that reduction permanent. Uncancelled shares can be resold or deployed for control, so the market prices a cancellation clause very differently from a bare repurchase pledge. Here is how to read the disclosures, the trust-contract loophole, and a checklist for judging any Korean buyback announcement.
A 2x daily-reset product does not double your holding-period return: after a +10% then -10% two-day swing, the underlying is down 1% but the 2x product is down 4%. Here is the reset mechanism, the decay math on volatile Korean names like Samsung Electronics and SK Hynix, and the FSC/KRX rules that govern these products.