KOSPI Surged a Record 17.91% in One Day — What SK Hynix's Limit-Up Really Means

A stock that had been cut in half within five days hit its daily limit the very next session — so what does this rollercoaster actually tell us?

What happened

On July 31, 2026, the KOSPI closed at 6,595.45, up 1,001.89 points (17.91%) from the previous session — the largest single-day percentage gain and point gain on record since the index was first calculated in 1980. It was also the first time the KOSPI had ever risen by more than 1,000 points in a single day.

The same day, SK Hynix closed up 29.95% at 1,718,000 won, hitting the exchange's daily price-move limit. That's the first limit-up for the stock since the band was widened from ±15% to ±30% in 2015, and its first limit-up of any kind since January 28, 2009 — 17 years ago. Samsung Electronics also jumped 26.81% to close at 262,500 won. Foreign investors were net buyers of a record 7.22 trillion won in KOSPI stocks that day, with more than half of that — 3.61 trillion won — going into SK Hynix alone.

Why now — the rollercoaster's backstory

To understand the surge, you have to start ten days earlier. On July 13, the KOSPI plunged 8.95% (669.01 points) to 6,806.93 amid Middle East geopolitical tension and a semiconductor sell-off, triggering the market's seventh circuit breaker of the year. SK Hynix alone fell more than 15% that day.

Sentiment then swung the other way: SK Hynix hit an intraday all-time high of 2,987,000 won on July 25, only to crash to 1,322,000 won by July 30 — down 54.7% from that peak in barely a month. What reversed the slide overnight was Microsoft's earnings beat and its reaffirmed AI capital-expenditure plans. With confidence in AI spending by major customers restored, buying flooded into the HBM (high-bandwidth memory) suppliers feeding that demand: SK Hynix and Samsung Electronics.

SK Hynix had just reported its biggest quarter ever for April–June: revenue of 79.32 trillion won and operating profit of 60.54 trillion won, a 76% operating margin. Revenue was up 257% and operating profit up 557% year over year, and first-half revenue topped 100 trillion won for the first time — driven by HBM and AI-server DRAM.

The numbers

What makes this rally "record-breaking" only becomes clear next to history. The previous record for a single-day KOSPI gain was 11.95%, set on October 30, 2008, at the height of the global financial crisis. This year's move beat that by nearly six percentage points.

Looking at SK Hynix's stock alone makes the whiplash of the past two weeks even clearer.

Industry estimates (citing TrendForce data) put SK Hynix's 2026 HBM market share at around 50%, with Samsung at 28% and Micron at 22%. UBS, however, expects Samsung to close much of that gap by 2027 — so whether SK Hynix stays this rally's biggest winner is still an open question.

The debate — real rebound or overheating?

Analysts are split. Hanwha Investment & Securities (4.3 million won), along with KB Securities, Shinhan Investment, Mirae Asset Securities and Daol Investment (4.2 million won each), have set SK Hynix price targets well above its current level, citing expanding long-term HBM supply contracts and continued AI server spending. Others have pulled back: Shinhan Investment cut its target from 4.2 million to 2.7 million won, and Hanwha from 4.3 million to 3.15 million won, reflecting worries about a memory-price peak and stretched valuations.

Some are more worried about the volatility itself. One analyst at an overseas bank compared the KOSPI's recent swings to a meme stock or cryptocurrency, arguing that a pattern of losing half its value in days and then hitting a limit-up the next day looks less like healthy price discovery and more like buy or sell orders piling up around a single moment and stock. Leveraged-product trading volume during the rally, in fact, fell to roughly a quarter of what it had been during the crash — suggesting plenty of retail investors sold at the bottom and missed the rebound.

What's next

Most brokerages expect a "stepwise" recovery through August. One forecast puts the KOSPI's worst-case support around 5,150, with resistance near 6,350 once uncertainty clears — a cautiously optimistic view that still leaves room for further pullbacks.

• The HBM race: Samsung has said it aims to lift its second-half HBM share to match its overall DRAM market share, making SK Hynix's ability to defend its lead the key thing to watch next earnings season.
• Retail and leveraged investors: if 30%-ish daily moves keep repeating, the swings for anyone holding leveraged or inverse products will be far larger than the index itself.
• Macro variables: Middle East geopolitical risk and the next round of Big Tech earnings and capex guidance remain the outside factors that will decide whether this rally has legs.

In the end, this KOSPI–SK Hynix rollercoaster says less about the "AI semiconductor supercycle" itself than about how much faster — and further — markets are now swinging in response to it.

This piece is nuloq's own analysis, built solely from the public reporting and official data listed under Sources, with the help of AI writing tools. Treat it as information, not investment, legal, or medical advice — it reflects the situation as of publication, and we'll correct it if we learn something was wrong.