Analysis
South Korea's Kospi index closed up 17.9% on Friday at 6,695.45, its largest single-day percentage gain on record, as a rally in chipmaking stocks erased most of a punishing three-day slide. Samsung Electronics surged 28% and SK Hynix jumped nearly 30% in the same session, together adding well over $100 billion in combined market value in a single day of trading in Seoul.
The move is a sharp reversal. The Kospi had sunk more than 17% over the prior three trading days as investors dumped technology stocks on fears of an AI infrastructure bubble and rising competition from Chinese chipmakers and AI labs. Friday's rebound was triggered directly by Microsoft's fiscal fourth-quarter earnings, released after Wednesday's US close, which showed Azure cloud revenue accelerating to 43% growth and a commercial backlog of $678 billion -- hard evidence, in the eyes of Asian investors, that hyperscaler AI spending is still converting into durable, contracted demand rather than speculative capacity.
The rally sits alongside a busy week for chip-adjacent names globally: Intel and AMD both jumped more than 12% and TSMC gained nearly 7% on Thursday after reports of a new advanced chip-packaging technology, while Nvidia's own market cap has oscillated between roughly $4.6 trillion and $5.1 trillion through the month as sentiment swings on hyperscaler capex commentary. Samsung and SK Hynix effectively form a memory-chip duopoly with Idaho-based Micron, and both companies' fortunes are now unusually correlated with a small number of quarterly reports out of Redmond, Mountain View and Cupertino.
“The company said it began mass shipments of HBM4 in the quarter and that first-half revenue crossed 100 trillion won for the first time in its history.”
The fundamentals underneath the rally are real and were already visible before Friday's bounce: SK Hynix reported record second-quarter operating profit of 60.54 trillion won, up 557% year-over-year, with an operating margin of 76%, driven by high-margin HBM memory for AI servers. The company said it began mass shipments of HBM4 in the quarter and that first-half revenue crossed 100 trillion won for the first time in its history. Samsung's semiconductor chief has told internal meetings that 2026 profit alone could exceed the company's cumulative profit from four decades in the chip business, as it races to expand HBM4E supply to Nvidia.
For founders and investors building AI infrastructure, the read-through is that memory economics -- not just GPU supply -- are now a binding constraint on the AI buildout. SK Hynix has said DRAM and HBM capacity is essentially sold out through 2026, and its CEO has warned the shortage could extend past 2030 as manufacturers keep reallocating fab capacity toward high-margin HBM at the expense of conventional DRAM. Any startup with hardware in its bill of materials -- from AI PCs to inference appliances to robotics -- should expect memory cost and lead-time volatility to be a live planning variable for years, not quarters.
The bear case is that Friday's record gain is itself evidence of how fragile sentiment has become: an index that can lose 17% in three days and gain 18% in one is not pricing in stability, it's pricing in extreme uncertainty about whether AI capex is sustainable, with each earnings call capable of swinging the answer sharply in either direction. SK Hynix's own results, despite being a record, still missed analyst consensus and initially sent its stock down nearly 10% -- a reminder that 'record profit' and 'beats expectations' are no longer the same thing in a market pricing in near-infinite AI demand growth.
What to watch next: Samsung's own detailed Q2 semiconductor results and HBM4E qualification progress with Nvidia, whether the Kospi rally holds through next week's session or proves to be a single-day dead-cat bounce, and whether Micron's next earnings call either confirms or complicates the memory-supercycle narrative that's currently driving both Korean chipmakers' valuations.
