Dual Catalysts Propel SK Hynix to 11% Gain as KOSPI Shatters Records

South Korea's KOSPI surged 8.42% on May 21, led by SK Hynix (+11%) after Nvidia earnings and Samsung labor resolution, highlighting sustained AI infrastructure demand.

South Korea’s benchmark index delivered a historic one-day performance on May 21, with SK Hynix at the epicentre of the surge. The memory chip maker’s shares jumped more than 11 percent, closing at 1.94 million won — a whisker below the all-time high reached on May 13. The rally was ignited by two simultaneous triggers: a blockbuster quarterly report from Nvidia and the resolution of a labour dispute at Samsung Electronics.

The KOSPI closed at 7,815.59 points, a gain of 606.64 points or 8.42 percent. That smashed the prior record for the largest single-day point advance, which stood at 490 points. Trading halts were triggered on both the KOSPI and KOSDAQ as volatility spiked. Samsung Electronics added over 8 percent on the day, and together the two chip giants represent roughly 49 percent of the entire KOSPI market capitalisation — their combined market value hit 3,133.6 trillion won.

Behind the fireworks was Nvidia’s latest earnings release. The US chip leader reported record revenue and profit, powered by data-centre spending and AI agents. SK Hynix is a crucial supplier of high-bandwidth memory (HBM) chips to Nvidia, and the quarter’s strength validated expectations that global investment in AI infrastructure remains on an unbroken upward trajectory.

Institutional investors drove much of the buying. During the trading session, they recorded net purchases of over 1.4 trillion won in SK Hynix alone. Retail shareholders, meanwhile, had been steadily pyramiding their positions in preceding months — building exposure as the stock climbed — a pattern that Samsung Securities says reflects deep conviction in the ongoing memory chip supercycle. Foreign investors, however, extended their selling streak to an eleventh day, creating a tension that some analysts warn may trigger a near-term pullback.

Since the start of the year, SK Hynix has gained roughly 186 percent. The stock’s 52-week low came in October 2025 at around 510,000 won, meaning it has nearly quadrupled from that trough. The company’s first-quarter 2026 results underscored the fundamental momentum: revenue topped 50 trillion won for the first time, both operating profit and margin hit records, and cash soared 19.4 trillion won quarter on quarter to 54.3 trillion won, while interest-bearing debt stood at just 19.3 trillion won. Management attributes the strength to AI infrastructure investment, including not only HBM but also high-capacity server DRAM modules and enterprise SSDs.

On the technology front, two SK Hynix executives received state honours on May 20 for semiconductor achievements, with the company linking the awards to progress on HBM4, 321-layer 4D NAND, and AI-focused memory. The firm is also developing custom HBM, high-bandwidth flash, and 3D-stacked DRAM on logic chips.

Nomura Securities has lifted its KOSPI target for 2026 to as high as 11,000 points, explicitly citing HBM demand as the main driver. For now, SK Hynix’s relative strength index sits near 69 — a level that signals a heating market. With foreign selling persisting, a rapid reversal from these elevated valuations is a distinct risk. On the supply side, SK Hynix is ramping capacity at its M15X facility and expanding the Yongin site. If demand for HBM and enterprise memory keeps pace, supply should remain tight. But any demand wobble would hit the stock with full force — and given its outsized weighting in the KOSPI, the index would amplify the swing.