❯ SK Hynix and Samsung Surge More Than 20% in a Day; KOSPI Logs Its Biggest Single-Day Gain on Record

RECORDKorea’s two major memory-chip makers surged in lockstep in Seoul on Friday — SK Hynix closed nearly 30% higher, touching its daily limit and posting its best session since its IPO, while Samsung Electronics closed up about 27%. The Korea Composite Stock Price Index rose 18% on the day, the biggest single-day gain in the index’s history, after having just shed 17% over the previous three sessions.

THE THREE-DAY DROPThe reversal began with the selloff early this week, when the market was digesting two things at once: worries that AI valuations were stretched, and signals of intensifying competition from Chinese memory-chip makers. After the 17% three-day slide, the strong overnight rebound in US tech stocks was the direct trigger, and SK Group Chairman Chey Tae-won’s purchase of additional shares in his own company was also read as a confidence signal. Japan’s market firmed in tandem, with SoftBank Group — which holds Arm and has long been treated as a proxy for AI exposure — up 13.8%. To be clear, a large part of the rally’s size reflects how steep the preceding drop was: down 17% in three days, up 18% in one. Together, the two numbers give the true picture of the week.

THE VOLATILITYA one-day 18% swing in the index shows that pricing of memory-chip stocks is no longer set by orders and capacity, but by confidence in how long AI capital spending can last. Bearing the brunt is the production-planning call for high-bandwidth memory: a market that spent the week swinging between “bubble” and “hoarding” cannot give factories a stable signal to expand capacity. South Korea’s financial regulator has already flagged the risks of leveraged ETFs.

▪ SIGNALDown 17% in three days, up 18% in one — this market is currently reporting sentiment, not prices.