South Korean Stocks Plunge 8% as Trading Halts Hit Both Markets and AI Financing Fears Spread

Seoul's stock rout triggers marketwide pauses

South Korea's two main stock markets fell more than 8% on Thursday, October 15, 2026, triggering circuit breakers as investors sold semiconductor shares amid renewed fears about US inflation and the cost of financing artificial intelligence projects.

The benchmark KOSPI was down 481.69 points, or 8.02%, at 5,527.12 at 12:52 p.m. local time. The KOSDAQ, which has a large concentration of technology companies, fell 66.07 points, also 8.02%, to 757.81. The Korea Exchange activated a circuit breaker on the KOSDAQ at 12:23 p.m. and suspended all KOSPI trading for 20 minutes at 12:38 p.m.

Samsung Electronics fell 9.7% and SK hynix lost 11.35% as selling intensified. Foreign investors sold South Korean shares, adding pressure to a market already heading toward its seventh consecutive session of losses. Closing prices and the total value of foreign selling were not yet available.

The immediate trigger came from the United States, where September consumer prices increased faster than expected. Investors feared that the Federal Reserve would keep borrowing costs high or raise interest rates again. Technology companies faced another concern: whether enormous spending on AI infrastructure would generate enough income to justify its cost.

The damage spread far beyond Seoul. Japan's Nikkei 225 fell 4.8%, while MSCI's broad measure of Asia-Pacific shares outside Japan dropped 3.3%. South Korea's decline was more than twice the percentage fall in that regional index, showing how heavily the selling struck its semiconductor sector.

How the trading day deteriorated

The KOSPI opened 5.59% lower at 5,673.01 and continued falling. Samsung Electronics began trading down 6.68%, while SK hynix opened 8.10% lower. Both chipmakers were heading toward a seventh straight session of declines.

The exchange first restricted certain automated orders before imposing the broader trading pauses. The sequence shows how quickly pressure built:

• 9:07 a.m.: A sell sidecar was activated on the KOSPI market, suspending program sell orders for five minutes.
• 9:12 a.m.: A sell sidecar followed on the KOSDAQ market.
• 10:08 a.m.: The KOSPI stood at 5,580.44, down 7.13%.
• 11:16 a.m.: The KOSPI was down 7.20% at 5,576.46, while the KOSDAQ had fallen 7.11% to 765.27.
• 12:23 p.m.: The KOSDAQ circuit breaker was activated.
• 12:38 p.m.: The exchange suspended all KOSPI trading for 20 minutes.

Both markets experienced circuit breakers on the same day for the first time since July 29, about 11 weeks earlier. Thursday also marked the first simultaneous activation of their sell sidecars since that date.

What the trading safeguards do

A sidecar and a circuit breaker interrupt different parts of the market. The KOSPI sidecar followed a fall of more than 5% in KOSPI 200 futures, contracts tied to the expected level of a major share index. It temporarily restricted program selling, in which computer systems place orders according to preset rules.

A circuit breaker reaches more widely by pausing trading across the affected stock market. Its purpose is to give buyers and sellers time to absorb information during an unusually sharp move. Thursday's KOSPI suspension lasted 20 minutes.

Selling was already broad before the full halt. During morning trading, 844 of the KOSPI market's 912 stocks were falling, or 92.5%, while only 61 were rising. Investors were selling across the exchange even as the largest semiconductor companies accounted for much of the attention.

The KOSPI had been declining since October 6. Thursday was also its third consecutive session trading below 6,000 during the day, following the initial break below that level on October 13.

Why American inflation hit Korean shares

US consumer price figures released on October 14 showed inflation running faster than markets expected. Rising oil and gasoline prices contributed, while price pressure also spread into goods and services beyond energy.

The Federal Reserve uses interest rates to influence borrowing and spending. Higher rates make loans more expensive and can slow price increases. They also raise costs for companies that need to borrow money to expand, including businesses building data centers and buying large quantities of AI equipment.

Wall Street had already absorbed those concerns before Asian markets opened. The S&P 500 fell 1.1% and the Nasdaq Composite dropped 1.9%, extending their declines to a third session. The Philadelphia Semiconductor Index fell for a sixth session, its longest losing run since May 2025.

South Korea's semiconductor manufacturers sit inside that global investment chain. Investors reassessed their shares as rising financing costs threatened the economics of the projects buying their products.

AI demand meets the cost of expansion

CoreWeave, a provider of computing infrastructure used for AI, became a focus of financing concerns. Its shares fell as much as 17% on Wednesday. Its bonds maturing in 2032 traded below 78 cents for each dollar of face value, compared with their original price at issuance four months earlier.

A bond is a loan investors make to a company. A price below 78 cents means investors were willing to sell that claim for less than 78% of its face value, a decline of more than 22% from the original level. Falling bond prices can make raising fresh money more expensive for the borrower.

Charu Chanana, chief investment strategist at Saxo Bank in Singapore, described the market's concern as a change in how investors value growth when funding is expensive.

"The sell-off in Asia looks less like a sudden deterioration in technology fundamentals and more like a repricing of the cost of capital," said Chanana.

Chanana explained why strong demand alone might no longer satisfy shareholders.

They are increasingly questioning what price they should pay for that growth when interest rates are high, volatile and potentially moving higher again.

Gartner estimates cited in the market discussion put US investment in AI infrastructure at about $1 trillion this year, followed by roughly $6 trillion more from 2027 through 2030. That later amount averages $1.5 trillion annually, compared with $1 trillion this year, illustrating the scale of funding that businesses would need to sustain.

Anthropic's slowing revenue growth, despite strong third quarter results presented to investors, added to the unease. Seo Sang-young of Mirae Asset Securities pointed to investors' growing focus on whether infrastructure spending becomes actual earnings and whether companies can continue financing it. JPMorgan analysts also identified financing risks and the timing of stock market listings as central concerns for AI shares.

Korean chipmakers face pressure on two fronts

Samsung Electronics and SK hynix faced both uncertainty over AI spending and growing competition from China. ChangXin Memory Technologies, known as CXMT, has been expanding production and making progress on a higher density DRAM design capable of storing more data.

DRAM is a type of memory that temporarily holds information while a computer works. More production from a competitor can increase supply and intensify competition over prices. For Korean memory manufacturers, that concern arrived as investors were already questioning how much customers could afford to spend on new computing capacity.

The losses extended into related companies. During morning trading, SK Square fell 11.38% and Samsung Electro-Mechanics dropped 15.21%. Those moves, alongside the large number of declining stocks, showed how widely investors were reducing exposure.

Broadcom chief executive Hock Tan had also warned that some AI investors were effectively gambling. His warning added to scrutiny of valuations and the gap between spending on infrastructure today and the income expected from it later.

The technology retreat spreads across Asia

Japan's Kioxia, another memory manufacturer, fell more than 11%, while SoftBank Group, a major AI investor, lost 9.4%. Taiwan's stock market dropped more than 3%, and Taiwan Semiconductor Manufacturing Company fell about 3% to around its lowest level in a month.

Hong Kong and mainland China also weakened. The Hang Seng fell 1.1%, China's CSI 300 lost 1.4%, and the Shanghai Composite declined 1.5%. Among individual technology companies, MiniMax fell 8.7%, Z.AI dropped 9.1%, Semiconductor Manufacturing International Corp. lost 4.5%, Baidu fell 4.4% and Alibaba declined 3.1%.

Indonesia and Singapore each lost about 1%. Singapore's DBS Group and OCBC also slipped about 1%, helping push the city state's shares to their lowest level in three months. Stocks in Malaysia and the Philippines edged lower.

TSMC's third quarter earnings, due later on Thursday, became an immediate test of the industry's outlook. The company was expected to report a sixth consecutive quarter of record profit, with investors watching its guidance for evidence that demand for AI chips could sustain growth.

A stronger dollar adds another strain

The South Korean won weakened 0.8% to 1,352.84 per dollar, its lowest level in two weeks. The Philippine peso reached a record low of 63.09 per dollar, while Taiwan's currency fell to 32.320 per dollar, its weakest level since early August.

A weaker local currency makes purchases priced in dollars more expensive. It also increases the local currency cost of repaying dollar debt. For companies already facing higher borrowing costs, that adds another demand on cash.

The US dollar index, which compares the currency with a basket of major counterparts, reached an 18 month high after the inflation figures before surrendering most of those gains in early Asian trading. MSCI's measure of emerging market currencies fell 0.4%, its worst session in two weeks.

China's yuan moved against the broader trend, edging higher to 6.6923 per dollar. Elsewhere, the Australian dollar declined 0.2% to $0.6956 after September employment unexpectedly fell by 39,300 jobs, compared with expectations for a gain of 20,000.

Rates, bonds and the next market tests

Investors increased their bets on another Federal Reserve rate rise, although expectations shifted during trading. One futures reading put the probability of an increase of 0.25 percentage points at the October 27 and 28 meeting at 31.6%, up from 22.1% a day earlier. A later CME FedWatch reading assigned a 75% probability to rates staying unchanged.

The Fed's benchmark range stood at 3.75% to 4.00% following September's increase. US producer price figures and retail sales data due later Thursday were the next scheduled tests of inflation pressure and consumer spending. Fed chair Kevin Warsh was also scheduled to speak in Bangkok on Friday with International Monetary Fund managing director Kristalina Georgieva.

Government bonds attracted buyers during the equity retreat. The yield on the US Treasury bond maturing in 10 years fell 7.8 basis points, or 0.078 percentage points, to 5.110%. Bond prices rise when yields fall. Investors were seeking protection from stock losses while also considering whether weaker growth might eventually restrain interest rates.

Mark Matthews, head of research for Asia at Bank Julius Baer in Singapore, offered a more optimistic view of the technology outlook.

"I'm not worried, because stocks are not expensive, there is no sign of a recession, and demand still massively exceeds supply in most parts of the AI story," said Matthews.

Thursday's immediate pressure nevertheless centered on financing: the price of borrowing, the ability to fund expansion and the earnings needed to support that spending. TSMC's results and the next US economic releases would give investors fresh figures to weigh before the Fed's October meeting.

Key Points

• The KOSPI and KOSDAQ each fell 8.02% during Thursday's session, triggering circuit breakers on both markets.
• Samsung Electronics lost 9.7% and SK hynix fell 11.35% as semiconductor selling intensified.
• Stronger than expected US inflation increased concern about borrowing costs and AI investment returns.
• CoreWeave's falling shares and bond prices brought AI financing risks into focus.
• The won weakened 0.8%, while Japan's Nikkei fell 4.8% and the regional MSCI index lost 3.3%.
• TSMC earnings, US economic data and the Fed's October 27 and 28 meeting were the next major scheduled tests.