KOSPI Sinks 1.79% as Samsung and SK Hynix Slide Past a 10 Trillion Won Buyback Wall

South Korea’s KOSPI closed 1.79% lower on August 28, dragged down almost entirely by its two heavyweight semiconductor names: Samsung Electronics ended the session down about 3% and SK Hynix lost more than 4%. The decline came despite one of the largest corporate share-repurchase campaigns in the market’s history — the two chipmakers have bought roughly 10 trillion won of their own stock in just seven trading days, with about 45 trillion won more still planned. The tech-heavy KOSDAQ, by contrast, finished slightly higher, underscoring how narrowly concentrated the selling was.

Two Stocks Moved an Entire Index

The session was less a broad retreat than a repricing of Korea’s semiconductor duo. Samsung Electronics and SK Hynix together dominate the KOSPI’s market capitalization, so a 3-4% move in the pair mechanically drags the benchmark down by well over a percentage point on its own. The KOSDAQ’s modest gain on the same day shows that smaller-cap investors were not running for the exits.

The concentration risk is structural. SK Hynix — which posted revenue of about 97.15 trillion won in 2025 — ranks alongside Samsung Electronics and Micron as one of the world’s three dominant memory-chip makers, meaning Korea’s main equity index effectively carries a leveraged position on the global memory cycle.

A Buyback Blitz That Could Not Hold the Line

What makes the drop notable is the buying pressure it overwhelmed. Over the preceding seven sessions, SK Hynix and Samsung Electronics repurchased approximately 10 trillion won of their own shares, and the companies have signaled plans to buy roughly 45 trillion won more. The scale of those purchases has been large enough to distort the market’s investor-flow statistics: the “other corporations” category of net buyers — the bucket that captures companies buying their own stock — swelled to unusual levels in Korea’s trading data.

Buybacks of that magnitude normally act as a price floor. On August 28 they did not, which suggests the selling — much of it from foreign and institutional accounts rotating out of chip exposure — was heavier than the repurchase programs could absorb on any single day.

Jackson Hole Caution After an Nvidia-Focused Week

Traders pointed to wariness ahead of the U.S. Federal Reserve chair’s Jackson Hole address as a likely trigger for the chip selloff, though the causation remains a matter of market interpretation rather than settled fact. The nervousness fits the week’s pattern: two days earlier, on August 26, the KOSPI hovered near flat as investors held positions ahead of Nvidia’s earnings release, a report that has become the de facto barometer for the AI-memory demand story underpinning both Korean chipmakers’ valuations.

The sequence — a flat wait for Nvidia, then a sharp two-stock drop into a Fed speech — reads as a market taking profits on its most crowded trade at the first sign of macro uncertainty, rather than a change in the underlying memory-demand outlook.

A Shareholding Filing Lands the Same Week

Adding a corporate-governance wrinkle, Samsung C&T submitted a large-shareholding report on Samsung Electronics to the Financial Supervisory Service’s electronic disclosure system. Filings of this type record changes in major holders’ positions or stake terms. Large repurchase-and-cancellation programs mechanically raise the percentage ownership of remaining shareholders even when they buy nothing, so Samsung’s buyback campaign gives the group’s ownership arithmetic — at a conglomerate led by chairman Lee Jae-yong — a reason to keep moving even on days when the share price falls.