A Chinese Memory Maker Rose 400% on Debut — Then Korea’s Market Broke

South Korea’s Kospi fell 10.84% on Tuesday, July 28, closing at 6,023.66 — a 732-point single-session loss that forced a marketwide circuit breaker and dragged Samsung Electronics down about 13.4% and SK Hynix about 14.5%, the worst single-day falls for both in close to two decades. Roughly $270 billion of market value was erased. Most coverage filed it under “AI selloff.” That framing misses what actually happened.

Three triggers, not one

The Seoul rout had three distinct catalysts converging in a single session, and only one of them was about AI sentiment in the abstract.

CXMT’s Shanghai debut. Chinese memory maker ChangXin Memory Technologies listed on the STAR Market after an $8.6 billion offering, and shares rose more than 400% on the first day. A domestic Chinese DRAM producer being valued that aggressively by its own capital market is a signal about expected future supply, not merely speculative froth.

Domestic DUV lithography entering service. China’s first domestically produced immersion deep-ultraviolet lithography machines went into service at SMIC and CXMT. DUV is the tooling category the West built its export-control regime around. Machines actually running in a fab is a different category of news from machines being announced.

The round-trip question. Overnight, Nvidia fell nearly 5% on renewed scrutiny of its financing arrangements with OpenAI, including reported consideration of guaranteeing roughly $250 billion for an Ohio data centre project while OpenAI separately weighs up to $350 billion in chip purchases. Critics call the structure circular.

Why this is a market-structure story

The Kospi’s problem is concentration. Two companies carry the index. When global sentiment toward chip valuations turns, investors do not need to sell Korea — they only need to sell Samsung and SK Hynix, and the index goes with them.

The mechanics were violent:

Metric	Value
Kospi close, July 28	6,023.66 (−10.84%)
Single-session points lost	about 732
Intraday low	5,992.91 — first break of 6,000 in about 3½ months
Kosdaq close	705.85 (−7.72%)
Rank by percentage decline	fourth-largest in Kospi history
Rank by points lost	second-largest in Kospi history
Marketwide circuit breakers in 2026	eight

Losses mounted from the opening bell. A sell-side sidecar triggered around 9:06 a.m. local time, and the Korea Exchange halted the main market for 20 minutes at 10:13 a.m. after the index held more than 8% below the prior close.

The SK Hynix wrinkle Canadians should notice

SK Hynix completed a $26.5 billion Nasdaq listing on July 10 — the largest US initial public offering ever by a foreign company, exceeding Alibaba’s 2014 debut. It sold 177.9 million American depositary shares at $149 under the ticker SKHY, and the stock opened at $170.

It first broke below the $149 IPO price around July 17, and it is below it again now. Anyone who bought the debut through a North American brokerage — including Canadians trading US-listed stock — is underwater on a position that was marketed as a blue-chip AI proxy at issue.

SK Hynix reports quarterly results on Wednesday, July 29: its first print as a US-listed company.

What it means for a Canadian portfolio

Direct Kospi exposure is rare in Canadian accounts. Indirect exposure is not. Broad emerging-market and developed-Asia ETFs hold Samsung and SK Hynix at meaningful weights, and global semiconductor ETFs are concentrated in the same handful of names. If you hold an all-world equity fund, you own this — and the portfolio tracker will tell you how much.

The transferable lesson is concentration risk, and Canada runs its own version: financials now exceed 25% of the TSX and account for nearly all of the index’s 2026 return. A market that looks diversified by ticker count can be badly undiversified by exposure.

Frequently asked questions

Why did the Kospi trigger a circuit breaker?
The Korea Exchange halts all trading for 20 minutes when the index stays more than 8% below the prior close for over a minute. That threshold was breached at 10:13 a.m. local time, following a sell-side sidecar at about 9:06 a.m. It was the eighth marketwide circuit breaker of 2026.

Does China’s DUV progress make ASML obsolete?
No. Domestic immersion DUV tooling entering service is a long way from matching ASML’s leading-edge EUV systems. The market reaction reflects the loss of a monopoly assumption at mature nodes, not a technical replacement at the frontier.

Is memory oversupply now the base case?
It is a live scenario rather than a tail risk. A well-capitalised domestic Chinese DRAM producer changes the outlook for commodity memory, though high-bandwidth memory for AI accelerators remains a tighter, more differentiated market.

How big was SK Hynix’s US listing?
$26.5 billion on July 10, 2026 — the largest US IPO by a foreign company on record, ahead of Alibaba in 2014.

Bottom line

The Kospi did not break because investors soured on AI in the abstract. It broke because a credible new supplier arrived, a tooling bottleneck looked less permanent, and an index built on two stocks had nowhere to hide.