Korea's stock market drops 5.5% as a Chinese memory breakthrough and Broadcom's 'casino' warning hit AI chip stocks

South Korea's Kospi closed down 5.46% on Tuesday, Oct. 13, 2026, its steepest drop since Aug. 19, as investors dumped the world's two biggest memory chip makers. The selloff followed Chinese memory maker CXMT's claim of progress on a denser DRAM design and remarks by Broadcom CEO Hock Tan at a Singapore conference on Monday comparing many AI investors to casino gamblers. Japan's Nikkei and Taiwan's market also fell, and memory maker Micron slid in early U.S. trading.

The AI trade has two load-bearing beliefs: that the spending will pay off, and that a few companies own the hardware it runs on. Tuesday both got poked at once. The man who sells custom AI chips to the biggest labs said out loud that a lot of the money is gambling, and China's memory champion said it's working on a way around the export controls meant to keep it behind. Note that CXMT hasn't shipped this chip, and Tan didn't say AI is a bubble; he said the investors don't understand it. Markets sold first anyway. When a country's stock market is basically two memory makers, a prototype announcement and one blunt quote are enough to erase 5% in a day. That's the real risk the AI boom has built: not that it ends, but that it's so concentrated that every rumor moves everything.

South Korea’s Kospi, the country’s main stock index, closed at 6,035.35 on Tuesday, Oct. 13, 2026, down 348.89 points or 5.46%, its steepest one-day decline since Aug. 19. Those closing figures are Seoul Economic Daily’s. Intraday it fell more than 7%, below 6,000 for the first time since late July, and the Korea Exchange briefly halted trading to curb volatility, its first such halt in two months. The index hit an all-time high above 9,000 in June. The halt and the June high are AP’s and MarketWatch’s.

Samsung Electronics closed down 7.39% at 232,000 won and SK Hynix closed down 10.09%. Those closes are Seoul Economic Daily’s. The two account for nearly half of the Kospi’s market value, MarketWatch reports. Foreign investors were heavy net sellers.

Elsewhere, The Guardian reports Japan’s Nikkei fell 1.8% and Taiwan’s exchange almost 2%, with TSMC down by a similar amount. Tokyo Electron fell 7.15% and SoftBank Group, an OpenAI investor, lost 8.5%. In early U.S. trading Micron slid 4.8%, AMD 1.4%, Nvidia 0.8% and Broadcom 0.2%, while the Dow rose. On Monday the Philadelphia Semiconductor Index, a basket of U.S. chip stocks, fell about 2.7%, MarketWatch reports. Those overseas and U.S. moves are The Guardian’s and MarketWatch’s.

One trigger: Chinese memory maker CXMT, ChangXin Memory Technologies, said it had made progress on a new DRAM architecture. DRAM is the memory that holds data while a computer is on, including the chips that feed AI servers. CXMT’s president, Cao Kanyu, said it would unveil a 4F² server DDR5 DRAM chip based on vertical surrounding gate technology within the year. The 4F² structure stacks cells vertically to raise density, a route around the EUV lithography tools China cannot buy. EUV, extreme ultraviolet lithography, is the machine that prints the finest chip patterns. CXMT gave no mass-production timing. Samsung and SK Hynix expect 4F² commercialization after 2028, and analysts say a 2026 product is likely a prototype. Goldman Sachs estimates CXMT’s capacity will reach 41% of Samsung’s and 50% of SK Hynix’s by 2028. Those lines are Seoul Economic Daily’s, The Guardian’s and Bloomberg’s.

The other trigger: Broadcom CEO Hock Tan, speaking Monday, Oct. 12, at the DBS Asia Future Forward Conference in Singapore, as Bloomberg reported. “A lot of investors have no clue what they are investing in.” They “set very extreme expectations only to find out that it’s almost like they are in a casino.” Tan said OpenAI’s $50 billion annualized revenue at the end of September suggests a viable business model but “doesn’t tell anything at this point” about long-term profitability because it is still losing money on training, and he said funding “might be the biggest constraint” on AI. On AI pilot projects he said: “Your parents give you $10 of tokens, you finish it in 10 minutes and you haven’t learned anything.” Intel CEO Lip-Bu Tan, at the same event, flagged rising capital costs. The Tan quotations are Bloomberg’s. The Intel line is Seoul Economic Daily’s.

IG’s Chris Beauchamp said “the rout in chip stocks seems set to continue thanks once again to news from China.” That quotation is The Guardian’s. Seoul Economic Daily reports the Kospi has dropped about 1,000 points in five sessions and notes foreign outflows ahead of Anthropic’s planned mid-November listing.

The picture is Broadcom’s official portrait of president and CEO Hock Tan, in a dark jacket and open-collared white shirt against a gray background. It is the company’s leadership photograph. The frame does not print a calendar date.

In plain terms, South Korea’s stock market fell 5.46% on Tuesday after investors sold Samsung and SK Hynix, the two companies that make up nearly half the index. CXMT said it is working on a denser memory chip that does not need machines China cannot buy. Broadcom’s CEO said a lot of AI investors are gambling. Japan, Taiwan and U.S. memory stocks followed the drop. CXMT has not said when the chip ships.