SKHX Slides as SK Hynix Eases Its HBM4 Ramp Into a Korea-Wide Rout

It Was the Tape, Not the Name

SKHX is down 14.83% over 24 hours to roughly $1,651, but the move starts in Seoul, not in anything SK Hynix did. The KOSPI closed down 9.99% at 8,203.84, shedding 910.71 points and tripping a market-wide circuit breaker for a 20-minute halt after sell-side sidecars had already fired earlier in the session. SK Hynix fell 12.47% and Samsung 12.31% — the two names that make up roughly half the index moved almost in lockstep, which is the tell. When a stock drops in line with its index and its closest peer during a foreign exodus of 5.79 trillion won, about $3.8 billion in a single session, the price action is about positioning, not a company-specific verdict. TradingKey framed it as a structural unwind of crowded long positions rather than an isolated chip story.

The HBM4 Wrinkle

There was a company-specific headline, and it's worth separating from the crash. On the same day, TrendForce reported that SK Hynix is slowing its HBM4 ramp while Samsung's HBM4 sales reportedly topped $1 billion — a genuine strategy split between the two. SK Hynix is pushing its HBM4 capacity expansion from Q2 into Q3 and redirecting resources toward conventional DRAM, where acute shortages have made commodity-memory margins more attractive than chasing HBM volume it doesn't immediately need. The key context: the company's 2026 HBM supply was already sold out earlier this year, and it shipped 12-layer HBM4E samples to customers on June 18. This reads as margin optimization from a position of strength, not a demand warning — and notably, it didn't make SKHX fall any harder than Samsung. If the market were punishing the HBM4 decision specifically, the two stocks wouldn't have moved together.

The Unwind Behind the Crash

The real story is a parabolic run meeting gravity. The KOSPI had been up more than 90% year-to-date and repeatedly hitting record highs, with SK Hynix among the year's biggest gainers on the AI-memory boom. At those levels the question stopped being whether the companies were executing — they were — and became whether the price had run ahead of even an optimistic reality. The trigger was external: weak US tech overnight and renewed worries about further Fed rate hikes after the Fed held rates but signaled a higher-for-longer path. The most telling detail is the split in flows — foreigners dumped $3.8 billion while retail investors bought a record net 11.11 trillion won, a standoff over whether the AI-memory trade is still intact. Micron's fiscal Q3 print, due the next day, sits on top of all of it as the next read on whether memory pricing is still climbing. Note that the bust-fear backdrop isn't new — analysts had been warning about memory's boom-and-bust cycle for weeks.

What the Dollar Perp Is Pricing

SKHX settles a Korean share in dollars, and that's why the 24-hour print reads 14.83% against SK Hynix's 12.47% close in Seoul. The perp tracks the won-denominated share price converted to USD, and the won sat near 1,540 per dollar — having weakened from around 1,508 as the dollar firmed on the Fed's higher path — so dollar holders wear FX on top of the equity move, and the rolling 24-hour window captures more of the slide than a single Seoul close does. With about $350 million in 24-hour volume on the HIP-3 market, there's enough depth to express the view either way, but the structure is worth internalizing: you're trading a Korean memory stock and the won at the same time. A stabilizing KOSPI doesn't fully clear the perp if the won keeps sliding.