The KOSPI's spectacular AI-fueled rally slammed into a wall as SK Hynix and Samsung dragged the index down nearly 10% in a single session
South Korea’s benchmark KOSPI index fell 9.99% on June 23, closing at 8,204 points in its steepest single-day decline in over three months. The sell-off was severe enough to trigger circuit breakers, halting trading for 20 minutes while the market tried to catch its breath.
The culprits were familiar names. SK Hynix and Samsung Electronics, the twin pillars of South Korea’s memory chip industry and the primary beneficiaries of the global AI spending boom, each dropped more than 12% on the day. When those two companies together account for roughly 40-50% of the entire KOSPI’s market capitalization, their bad days become everyone’s bad days.
A rally that doubled, then stumbled #
The KOSPI had surged more than 100% year-to-date by June 2026, peaking above 9,000 points. The rally was almost entirely driven by demand for advanced memory products used in AI data centers and training infrastructure, which sent SK Hynix and Samsung’s valuations soaring, dragging the entire KOSPI along for the ride.
The Kospi 200 Volatility Index, South Korea’s equivalent of Wall Street’s VIX “fear gauge,” spiked to around 75. Normal readings hover around 20.
What spooked the market #
The June 23 plunge wasn’t an isolated event. The KOSPI had already experienced violent swings in the preceding trading sessions, including drops of 8-9% followed by rapid rebounds.
South Korean regulators have increased scrutiny of leveraged trading products. Leveraged instruments amplify gains on the way up and losses on the way down, and regulatory tightening in this area could cool speculative enthusiasm.
What this means for investors #
For investors with direct exposure to the KOSPI, or to SK Hynix and Samsung individually, the concentration risk is impossible to ignore. When two companies represent roughly half of an index’s market cap, a 12% drop in those two names mathematically guarantees a severe index-level decline, regardless of what every other listed company does that day. The demand for advanced memory chips isn’t fiction. AI workloads genuinely require massive amounts of high-bandwidth memory, and SK Hynix and Samsung are genuinely the dominant suppliers. But there’s a meaningful difference between “this is a good business” and “this business justifies a 100% year-to-date index return.”
If South Korean authorities continue tightening rules around leveraged products, some of the speculative capital that fueled the rally could exit, removing a key source of buying pressure. Disclosure: This article was edited by Editorial Team. For more information on how we create and review content, see our