SK Hynix plunged 15.4% in Seoul on Monday, its largest one-day decline on record, as profit-taking swept through one of the world’s most crowded AI trades.
The stock closed at 1.845 million won, down 335,000 won from Friday. Samsung Electronics fell more than 10%, helping drive the KOSPI down nearly 9% and triggering a 20-minute market-wide trading halt.
SK Hynix shares had more than tripled during 2026 before the latest pullback, powered by rising high-bandwidth memory demand and the company’s position as a key supplier to Nvidia and other AI infrastructure groups.
The sharp reversal hit a market already heavily concentrated in memory stocks. SK Hynix, Samsung and Micron account for roughly three-quarters of the Roundhill Memory ETF, which recently passed $25 billion in assets after attracting more than $20 billion since its April launch.
Nasdaq Debut Rally Reverses In Seoul
The selloff came one trading day after SK Hynix completed a $26.5 billion U.S. share sale, one of the largest equity offerings ever completed in the American market.
Its Nasdaq-listed American depositary receipts were priced at $149 and opened at $170 on Friday before finishing their first session 12.8% higher at $168.
The Seoul decline left the U.S. securities trading at a roughly 37% premium to the Korean shares. Ten ADRs represent one SK Hynix common share, but conversion restrictions limit the arbitrage that would normally narrow the valuation gap.
A twice-leveraged SK Hynix exchange-traded fund listed in Hong Kong lost more than one-third of its value during Monday’s session as products built around the memory rally amplified the reversal.
HBM4 Shipments Add To Earnings Caution
Investors also cut positions ahead of SK Hynix’s second-quarter results as expectations around next-generation HBM4 shipments softened.
The market had expected HBM4 deliveries to increase during the second quarter, but the planned ramp has not yet appeared at scale. SK Hynix may also capture less of the latest rise in conventional DRAM prices than Samsung because a larger share of its business is concentrated in high-bandwidth memory.
SK Hynix controlled 58% of global HBM revenue during the first quarter, compared with 21% each for Samsung and Micron.
The company signed a multiyear AI memory partnership with Nvidia in June covering future HBM products, AI systems and semiconductor manufacturing tools. Its Korean shares remain nearly 600% higher than a year ago despite falling about 38% from their late-June record.
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