Seoul’s trading floor had a bad Tuesday. The Kospi closed down 5.46% at 6,035.35, its steepest one-day fall since August 19, after sliding as far as 5,911.11 during the session, a drop of 7.41% from the prior close. A sell-side trading curb kicked in at 9:47 a.m., the first such pause in nearly two months, according to KED Global.

The selloff followed three separate pieces of news that landed within about 72 hours. Each one touched the same nerve: how much confidence the AI boom deserves.

The Memory Makers Took the Hit

The sharpest pain was in memory chips. Samsung Electronics and SK hynix, the two companies that supply much of the memory inside AI data centres, led the Kospi lower. Their closing declines differ by outlet. AJP reports Samsung down 6.79% and SK hynix down 9.47%, while Korea JoongAng Daily puts the figures at 7.39% and 10.09%. Either way, SK hynix finished the day down roughly nine to ten percent.

Foreign investors were heavy sellers. AJP reports net foreign selling of 4.53 trillion won (about US$3.4 billion) across Kospi shares, the largest since July 28. That figure appears only in AJP’s reporting.

Tuesday’s rout built on Monday’s. Samsung and SK hynix had already fallen about 4.4% and 4.5% in Asian trading on October 12. In the US that day, the Philadelphia Semiconductor Index lost 2.67% to 12,236.79 and Micron dropped 3.88%. The broader market barely noticed. The S&P 500 slipped 0.06% and the Nasdaq Composite fell 0.44%, while the Dow rose 0.38%, per CNBC. The pain was concentrated in chips.

A Chinese Rival Says It Has Cracked Denser Memory

The first trigger came from Shanghai. At the fourth Integrated Circuit and Chiplet Conference on October 9 and 10, China’s CXMT said it had made “key progress” on a new cell architecture that raises memory density. Its president, Cao Kanyu, said a server-memory product built on it is planned by the end of 2026. SCMP’s coverage describes the move as work on a design Samsung and SK hynix are also chasing.

The product is a DDR5 RDIMM server module using what the industry calls a 4F² cell structure. Mainstream commercial DRAM today uses a 6F² layout. In theory, 4F² can shrink cell area by 33% and fit 50% more cells into the same space. SK hynix unveiled its own 4F² roadmap in 2025, and Samsung has reportedly aimed for mass production using the design by 2028.

Treat the announcement with some care. CXMT disclosed no detailed specifications and no launch date. This is a company statement, not a shipping product. Critics quoted by Seoul Economic Daily point out that producing such chips reliably at scale is a separate challenge from announcing them. Still, markets do not wait for proof. The prospect of a Chinese competitor narrowing the gap in server memory was enough to hit the incumbents’ shares.

Broadcom’s CEO Compares Some AI Investing to Gambling

The second jolt came on Monday in Singapore. Speaking at the DBS Asia Future Forward Conference, Broadcom CEO Hock Tan said capital would be the biggest constraint on AI development going forward. According to Reuters’ report on the remarks, he described investors as setting extreme expectations, “almost like they are in a casino gambling.”

The source of the comment matters. Broadcom is one of the biggest beneficiaries of AI spending. It reported $16.7 billion in AI semiconductor revenue for its fiscal third quarter, up 221% from a year earlier, and guided to $21.7 billion for the fourth. It has also forecast $230 billion in annual AI chip revenue by fiscal 2028, according to figures carried by Benzinga and Yahoo Finance. When a company with that kind of order book says parts of the investment flow look like a gamble, traders listen.

Reporters have pointed to Tan’s remarks, the CXMT news and foreign selling as contributors to the Korean slide. That causation is the outlets’ reading, not something anyone has proven. One analysis noted that the selloff appears to reflect sentiment rather than any revision to AI demand forecasts.

Then the IMF Weighed In

The third piece arrived Tuesday, as finance officials gathered for the IMF-World Bank Annual Meetings. In its latest Global Financial Stability Report, the IMF found that markets have been resilient but that stability risks remain elevated. It named three “salient risks”: an AI-driven market correction, a further sharp rise in sovereign bond yields, and cyber threats. The IMF’s own announcement sets out the findings.

The report framed these as “plausible near-term catalysts for a sharp tightening of financial conditions,” in wording carried by RTÉ. On AI specifically, it warned that weaker investment and profitability could be “a shock that triggers a market correction,” as reported by Channels TV.

Athanasios Vamvakidis, a deputy director in the IMF’s Monetary and Capital Markets Department, spoke to reporters after the launch about cyber risks. He described them as “known and very much unknown,” according to Kuwait Times. Several outlets appear to have carried the same wire copy, so the IMF’s own materials are the reliable reference.

What to Watch Next

The coincidence of timing is what made the day so rough. A rival’s technical claim, an insider’s blunt comment and an institutional warning each said something different. Together they hit a market that had priced in a great deal of AI optimism.

Near term, attention turns to US consumer price data due Wednesday. Korea JoongAng Daily notes it could offer clues on the Federal Reserve’s October rate decision. The date of the Fed meeting itself has not been verified.

The longer test belongs to CXMT. Its end-of-2026 target for a 4F² server module, with no date attached, will show whether the “key progress” turns into product or stays a headline. Until then, Korea’s memory makers and the investors who hold them are left weighing a question the IMF, a chip executive and a Chinese rival all raised in the same week: how much of the AI buildout is demand, and how much is expectation?