Samsung and SK Hynix Fell 4%; China's CXMT Is Moving Into Server Memory

Seoul's stock market posted its lowest close in two months on Monday. The Kospi fell 241.69 points to 6,384.24, and the Kosdaq lost 4.83%.

Two memory makers did most of the damage. Samsung Electronics fell 4.39% to ₩250,500 (about $188), and SK Hynix fell 4.52% to ₩1,605,000 (about $1,202).

Foreigners Sold, Retail Investors Bought

Figures are converted at the closing rate of about ₩1,335 per dollar. Foreign investors were net sellers for a fifth straight day, dumping about $1.5B of shares. Individuals bought $1.1B.

The index has lost 619.50 points, or 8.85%, in four sessions since Oct. 6. Yuanta Securities' Lee Jae-won said the market's biggest problem is not chip earnings but foreign fund flows.

Sources cite several causes. These include higher oil after weekend Houthi strikes on Riyadh's airport, elevated U.S. Treasury yields, the possible end of both companies' buybacks and a rebalancing of chip ETFs. None of them weighs these factors against each other.

What CXMT Announced Over the Weekend

The new item on the list came from China. CXMT President Cao Kanyu told an industry conference in Shanghai on Saturday that the company will launch a 4F²-based DDR5 RDIMM server memory product before the end of 2026.

TradingKey tied the intraday 4% drop in Samsung and SK Hynix to the announcement. Closing reports from Korea JoongAng Daily and Financial News did not mention CXMT. The announcement is a roadmap, not a product.

Samsung is expected to move to 4F² production in 2028. None of the three big makers has commercialized the architecture at scale.

The market did not read this as a technology story. It read it as a pricing story.

Why the Square Cell Matters

In DRAM, F is the finest line a chipmaker can draw. Today's cells occupy 6F² of area; 4F² is a tighter layout using the same line.

Drawing finer lines requires EUV machines, and China has had no access to them since 2019. 4F² raises density by changing the layout, not by thinning the line. Sources do not draw this link for CXMT specifically, but the geometry points to a route around export controls.

CXMT targets capacity of 300,000 wafers a month across three fabs by year-end. Two plants under construction could lift that to 600,000. Its customers have so far been mostly in consumer electronics.

The Part That Does Not Fit

Memory prices are not falling. TrendForce expects conventional DRAM contract prices to rise 10-15% in the fourth quarter. That is slower than the roughly 60% jump in the second quarter, but the direction is the same.

Mirae Asset's Kim Seok-hwan told Reuters the issue is not demand: "The market's focus has shifted to whether the sharp earnings growth that started a year ago would be sustainable."

CXMT's product is also untested. There is no data on speed, capacity or customer qualification. In February, former SK Hynix vice president Shim Dae-yong sized the gap this way: "The gap is not two or three years. In my view, it is more than five."

In the U.S., Micron is the stock most directly tied to contract prices; its last three months are below (earnings analysis).

The Nasdaq 100's past month frames the pressure that yields and oil have put on tech stocks broadly.

What It Means for Investors

• The market priced the duration of the earnings boom and the prospect of a fourth server DRAM supplier, not a drop in memory prices.
• For Micron, SanDisk and Western Digital, the risk is the price of contracts renewed in 2027-2028, not volume; CXMT in servers adds a party to that negotiation.
• Dates to watch: ASML on Oct. 15, SK Hynix on Oct. 27 and Samsung on Oct. 29, including Samsung's buyback and shareholder-return plans.
• The risk that would break the thesis is a major server maker qualifying CXMT's 4F² memory around year-end, which would push its cost-per-bit edge into prices.

Sources: Oct. 12 Kospi closing reports from Korea JoongAng Daily, Financial News and Digital Today; Oct. 11 reports on CXMT's 4F² announcement from Global Times, TweakTown and WindowsForum; Counterpoint share data. The TrendForce forecast and the Reuters comment are as relayed by Invezz; Shim Dae-yong's view is from a Feb. 2, 2026 Korea Herald interview. Weekend geopolitical developments are from a Euronews report based on AP and AFP. CXMT's technical claims have not been independently verified.