South Korea's Kospi closed nearly 18% higher on 31 Jul, the biggest single-day gain on record, as a rebound in semiconductor stocks reversed three sessions of losses. The index has topped a 10% daily gain only once before, on 30 Oct 2008, when it rose 12% on news of a US currency swap during the global financial crisis. This time it cleared that mark on a rebound alone.
Kospi Notches Record Surge as Crypto Perps Saw It Coming
31 July 2026 - 11:43 UTC
By Oihyun Kim
The surge followed better-than-expected cloud earnings from US hyperscalers such as Amazon, Meta and Microsoft, easing fears that spending on artificial intelligence had outrun demand. These hyperscalers, which build and run their own data centres, are among the biggest buyers of the memory chips made by SK Hynix and Samsung Electronics, the two largest stocks on the Kospi.
Volatility runs both ways
Today's surge is just one face of the Kospi's recent turmoil. The index has swung more than 3% up or down on 13 of the past 21 trading days, and four automatic trading halts have been activated this month, about a third of the index's all-time total.
Kim Hak-kyun, head of research at Shinyoung Securities, told Maeil Business, a Korean daily, that the volatility would not subside: "This is a road not travelled; the volatility is structural."
He named China as a lasting risk. In every industry it has entered, he said, margins have collapsed because firms are not run for profit and the state funnels in support. If AI goes the same way, the capital spending by US hyperscalers that is now driving demand for Korean memory chips may not last, leaving investors in the chipmakers exposed.
Hynix hits its ceiling
SK Hynix, the second-largest Kospi stock, closed at its 30% daily price limit, its first limit-up close since the ceiling was widened to 30% in June 2015, finishing at 1.72mn won ($1,205).
SK Group chairman Chey Tae-won disclosed on 30 Jul that he had bought about 4.9bn won ($3.4mn) of SK Hynix shares, his first purchase of the stock in his own name.
Kospi's biggest stock, Samsung Electronics, closed 27% higher for a record daily gain, while SK Square, SK Hynix's largest shareholder, also finished limit-up at 1.04mn won ($728). Overnight in the US, Micron gained 18% and SanDisk 26%.
Offshore priced it early
The rally showed up first offshore, on perpetual futures: crypto derivatives with no expiry that trade around the clock, known as perps. Those tracking SK Hynix began climbing after Seoul closed on 30 Jul, previewing the limit-up while the cash market was shut, then kept rising once the cash market hit its ceiling.
On Binance, a traditional-finance (TradFi) Hynix perp last traded 27% higher (06:30UTC on 31 Jul, per Binance), while Hyperliquid's permissionless market tracking the same stock was up 30% on turnover of more than $1.5bn (06:30UTC, per Hyperliquid).
Seoul's cash market is now shut for the weekend, more than 65 hours until Monday's open. The perps will keep pricing Hynix through the gap.
