South Korea's Kospi index fell more than 7% in a single session, with semiconductor shares driving the sell-off as investors rethought the durability of the AI boom, KTVN reported.

The drop ranks among the sharpest single-day declines for the benchmark in recent memory. And chips did the damage. Seoul's index leans heavily on its two memory giants, Samsung Electronics and SK Hynix, whose fortunes ride on AI-driven demand for high-bandwidth memory and advanced logic. When that thesis wobbles, the whole market feels it.

What triggered the sell-off?

According to the report, the rout centered on semiconductor shares as worries mounted that the AI boom — the engine behind Korea's chip export strength — may not sustain the growth investors had priced in. The fear isn't abstract. Korean chipmakers have spent the past two years betting capital and capacity on AI-related memory demand. Any signal that hyperscaler spending could slow hits their valuations first and hardest.

Korea's benchmark is unusually concentrated. Samsung and SK Hynix together anchor a outsized share of Kospi weighting, so a sector-wide repricing of semiconductor stocks translates almost mechanically into an index-level move of this magnitude. A 7% fall isn't just bad sentiment. It's the market repricing its single largest earnings engine.

Why do AI doubts hit Korea hardest?

The AI trade has been generous to Korean chipmakers. Memory suppliers have ridden datacenter buildouts and accelerating high-bandwidth memory demand to strong results. That same dependence cuts both ways. If investors start questioning how long AI infrastructure spending can run at current levels, Korea's chip complex becomes one of the most exposed equity stories in Asia.

Monday's move suggests that questioning has begun. A sell-off of this size signals a broad shift in positioning, not a single-stock stumble. Traders dumped semiconductor names across the board, dragging the Kospi down more than 7% before the session closed.

What comes next?

The report doesn't forecast a floor, and neither will we. But the mechanics are clear: Kospi's direction in coming sessions will track two things — whether AI capex signals from major cloud and chip customers hold firm, and whether Korean memory makers can defend their pricing and shipment outlooks. Until one of those anchors moves, volatility of this scale stays on the table.