KOSPI Crashes 5% and Triggers a Sell Halt: Asia's AI Rout Explained

South Korea's KOSPI plunged more than 5% on Friday, October 30, 2026, triggering an emergency five-minute halt to program selling, as a Wall Street rout in artificial-intelligence stocks — led by Alphabet's 12.6% plunge on Thursday — slammed Asia's biggest chipmakers. Samsung Electronics fell about 6% and SK hynix dropped more than 8% in Seoul, Japan's Nikkei fell over 2%, and Taiwan's Taiex shed around 3%, even though the Korean chip giants had just reported record profits.

What happened in Seoul?

The KOSPI opened 2.99% lower and kept falling through the morning. By 11:20 a.m. in Seoul it was down 311.84 points, or 5.25%, at 5,626.02, according to Yonhap News Agency. Shortly after 10 a.m., the Korea Exchange activated a sell-side sidecar — a five-minute suspension of program sell orders — after KOSPI 200 futures fell 5% or more for at least a minute, the trigger for the safeguard.

The index later recovered part of the loss and closed 3.96% lower, CNBC TV18 reported — still one of its worst sessions of the year, and a violent reversal after the KOSPI had surged a combined 9.93% over two sessions through Wednesday.

Which stocks led the fall?

The selling was concentrated in the two heavyweights that dominate the index. Samsung Electronics fell 6.03% and SK hynix plunged 8.65% late in the morning, Yonhap reported. Hyundai Motor slipped 3.76% after cutting its annual sales target, and Hanwha Aerospace slumped 12.24% after weaker third-quarter earnings and delays in K9 howitzer deliveries to Poland.

The rout spread across the region. Japan's SoftBank Group slid about 6.5%, the Nikkei Stock Average fell about 2.2%, and Taiwan's Taiex shed about 2.2% to 3%, Dow Jones Newswires reported via Morningstar. Hong Kong's Hang Seng was an outlier, rising as mainland China's Shanghai Composite slipped.

Why is it blowing up?

The trigger came from the United States. Alphabet, Google's parent, plunged 12.64% on Thursday — losing roughly half a trillion dollars in market value — after its third-quarter revenue fell short and heavy AI spending pushed free cash flow negative. The Nasdaq Composite fell 1.4% on Thursday, and results after the close from Amazon and Intel added to the gloom.

That matters enormously for Korea. Samsung and SK hynix supply the memory chips used in AI data centres, so their earnings depend on hyperscalers such as Alphabet, Amazon and Microsoft continuing to spend. When investors start questioning whether that spending will earn its keep, Korean chip shares are among the first places the doubt shows up — and because the two companies carry such large index weights, their falls drag the whole KOSPI with them.

The paradox at the centre of the rout is that the fundamentals just printed were record-breaking. Samsung reported third-quarter operating profit of 107.4 trillion won this week, and SK hynix posted a record 83.33 trillion won. Neither result protected the shares: foreign investors sold heavily anyway, a sign the market is now pricing the risk that the AI capital-spending cycle slows, rather than rewarding the profits it has already produced.

Key facts

• KOSPI intraday low: down 5.25% at 5,626.02 late Friday morning; close down 3.96%.
• The Korea Exchange's sell-side sidecar halted program selling for five minutes after KOSPI 200 futures fell more than 5%.
• Samsung Electronics fell about 6% and SK hynix more than 8% in Seoul.
• Japan's Nikkei fell over 2%, Taiwan's Taiex fell about 3%, and SoftBank slid about 6.5%.
• The catalyst was Alphabet's 12.6% Thursday plunge in New York on a revenue miss and negative free cash flow tied to AI spending.

Sources: Yonhap via Korean-Vibe, Dow Jones via Morningstar, Reuters, CNBC TV18 via TradingView.

What's next?

Attention now turns to whether US technology shares stabilise when New York opens on Friday, and whether the next round of hyperscaler results reassures investors about AI returns. For Seoul, the close well off the intraday low suggests some buyers stepped in once the sidecar slowed the selling, but a market that can fall 5% in a morning on another country's earnings miss is likely to stay volatile while the AI-spending debate runs. This article reports market movements only and is not investment advice.

FAQ

Why did the KOSPI fall more than 5% on October 30, 2026?

It fell after Alphabet plunged 12.6% in New York on AI-spending concerns, triggering heavy foreign selling of Korean chip stocks Samsung Electronics and SK hynix, the index's biggest weights.

What is a sell-side sidecar?

It is a Korea Exchange safeguard that suspends program sell orders for five minutes when KOSPI 200 futures fall 5% or more for at least one minute, designed to slow disorderly selling.

How did Samsung and SK hynix shares perform?

Samsung Electronics fell about 6% and SK hynix more than 8% during the session, despite both companies having just reported record third-quarter operating profits.

Did other Asian markets fall too?

Yes. Japan's Nikkei fell over 2%, Taiwan's Taiex shed about 3%, and SoftBank slid about 6.5%, while Hong Kong's Hang Seng rose against the trend.