South Korea's KOSPI closed up 17.91% at 6,595.45 — a gain of 1,001.89 points on Friday, the biggest single-day rise in the index's history, beating the record it set during the 2008 financial crisis (per TradingKey).

Almost all of that came from two stocks. SK Hynix locked limit-up at +30% and Samsung Electronics closed about +27%. Those two are more than half of the KOSPI's weight and over 60% of the listed market's profits — when they rip, the index rips. So the real question is why they ran.

What lit the fuse

Two US earnings prints flipped the mood overnight. Microsoft jumped 15.5% Thursday (its best day in ~18 years) on ~$90B revenue and 43% Azure growth, and Amazon's AWS grew 37% with management flagging ~$220B of 2026 capex and AI capacity effectively sold out into 2027. For Korea's memory makers that's the whole ballgame: the companies buying HBM and DRAM are still short of chips, so the "AI spending is peaking" scare that crushed the tape last week just got contradicted by the biggest spenders themselves.

A local kicker helped SK Hynix specifically: SK Group chairman Chey Tae-won personally bought its shares — a rare insider vote of confidence (KED Global). Underneath it all, June chip exports were up 199.5% YoY to a record $44.8B, and foreign investors net-bought roughly ₩7 trillion, one of the largest single-day buys on record.

Remember the setup: this erased a genuinely brutal week. The KOSPI had fallen more than 17% over three sessions — tripping two circuit breakers — and was down ~22.4% for July, roughly 41% below June's 9,385 peak, on fears that China's CXMT would flood the DRAM market.

The ripple: the cleanest listed read-through is Micron (MU), which popped ~18% Thursday on the same signal. Same logic — if DRAM and HBM stay supply-constrained into 2027, Micron books a higher price per bit on every chip it ships. Tokyo Electron (+11%) and Taiwan's Taiex (+7%) moved on the same memory-shortage thesis.

The risk that flips it: this is still a relief bounce inside a bear market. At 6,595 the KOSPI sits ~30% under June's peak and runs straight into resistance near 6,983 (its 50-day EMA). If it can't reclaim that level in the next few sessions, today's rip is a dead-cat inside the China-competition downtrend, not a turn. Watch 6,983.

As of Fri 31 Jul 2026, ~7:35pm IST. Sources: TradingKey, KED Global, AP. For discussion and education only — not investment advice. Verify before acting.