Samsung and SK Hynix Slide as Chinese Memory Maker CXMT Signals a Denser 4F-Squared DRAM Design

A weekend progress report from a Chinese memory chipmaker that most of the world had never heard of until July set off a global semiconductor sell-off on Tuesday, and the damage landed hardest on the two companies that dominate the memory market. Samsung Electronics fell 7.4% in Seoul and SK Hynix closed 10% lower, and because the pair together account for roughly half of the Kospi's total market capitalization, South Korea's benchmark index slid more than 5% and briefly triggered the exchange's Sidecar mechanism, which pauses program trading for five minutes.

The trigger was ChangXin Memory Technologies, or CXMT. The Hefei-based DRAM maker said it had made significant progress on a next-generation memory cell architecture known as "4F²," which packs storage cells into a smaller footprint than the mainstream 6F² layout — in principle shrinking the area of a single cell by about a third and raising density on the same silicon. The company plans to apply the design to a server-grade DDR5 RDIMM product by the end of 2026, placing it squarely in the data-center memory segment that has been the backbone of the AI infrastructure boom.

The sell-off spread well beyond Seoul. Micron, SanDisk, Seagate and Western Digital all slid in US premarket trading, Tokyo Electron fell more than 7% and SoftBank Group, an OpenAI investor, lost 8.5%. In Europe, ASML dropped more than 3% while STMicroelectronics and Infineon lost about 5% each. The Philadelphia Semiconductor index has now fallen more than 7% from its October high.

CXMT is a comparatively new name on the global stage. It listed on Shanghai's STAR Market in July and surged nearly 466% on its debut, briefly becoming the most valuable company on the board. Its market capitalization stands at roughly 3.46 trillion yuan, about $520 billion and not far below Tencent. Its share of the global DRAM market has climbed to around 10% from roughly 4% a year ago, according to an HSBC note, and Apple has reportedly been testing its DRAM for devices sold in China.

Wall Street's mood was not helped by Broadcom chief executive Hock Tan, who told a conference in Singapore that many investors in the AI buildout "have no clue what they are investing in" and set "very extreme expectations only to find out that it is almost like they are in a casino." He noted that OpenAI's annualized revenue of about $50 billion suggests a viable business but offers little assurance about long-term profitability while training spending continues.

Analysts were quick to pour cold water on the panic. Kiwoom Securities' Han Ji-young noted that a technical announcement is not a mass-production success, and that CXMT still has to clear yield, performance and customer-qualification hurdles — with US export controls keeping EUV lithography out of reach. UBP's Vey-Sern Ling called the moves profit-taking on crowded memory winners, and Rayliant's Phillip Wool argued the reaction was disproportionate given that CXMT has yet to demonstrate volume production and trails in HBM, the memory that matters most for AI accelerators. SK Hynix, for its part, has its own roadmap for 4F²-class designs.

What the episode really measures is how tightly wound the AI trade has become. Memory pricing power is one of the load-bearing assumptions of the infrastructure buildout, and the market has shown it will reprice that assumption on a single corporate statement — before a single 4F² module ships. If CXMT converts the announcement into qualified server memory on schedule, the argument gets harder to dismiss; if it slips, Tuesday's losses will look like noise.