South Korea's KOSPI index plunged more than 8% on July 28, 2026, triggering an exchange circuit breaker as a broad AI-driven selloff hammered chipmaking stocks across Asian markets. The KOSPI fell to a three-month low. Japan's Nikkei 225 closed down 4.3% at 62,127.57, and Taiwan's Taiex skidded 3.9%.

The selloff centered on the semiconductor names that have been the primary beneficiaries of the AI infrastructure buildout. Samsung Electronics shares dropped 13.4%, according to Reuters. SK Hynix fell as much as 10%. The two companies are Korea's dominant memory chipmakers and among the most heavily weighted components in the KOSPI. When stocks of that size move double digits in a single session, the index mechanically follows.

The trigger was not a single data point but a confluence. Reuters reported that Samsung and SK Hynix slid amid Nvidia financing worries and China competition concerns. The selloff also occurred ahead of major Big Tech earnings releases, per Investing.com, adding an event-risk premium to already fragile positioning. Market participants facing binary earnings outcomes on their largest holdings chose to reduce exposure first.

The circuit breaker activation is itself worth noting. These mechanisms are designed to halt trading temporarily when indices move beyond predefined thresholds, giving the market a cooling-off period. When they trigger, it signals that selling pressure overwhelmed normal order-flow absorption. That the KOSPI hit this level indicates the selloff was not a gradual drift but an acute, concentrated deleveraging event in one of Asia's most liquid markets.

The regional breadth was broad. The Nikkei 225's 4.3% decline to 62,127.57, per The Washington Post, confirms the rout extended well beyond Korea. The Taiex's 3.9% drop, reported by AP via informnny.com and semissourian.com, brings TSMC's home market into the same pressure zone. Three major Asian indices falling 4% or more on the same day, all with chip-stock exposure as the common thread, marks a coordinated sector deleveraging.

What separates this from ordinary risk-off rotation is the specific vulnerability of the AI supply chain. Memory chipmakers like Samsung and SK Hynix supply HBM (high-bandwidth memory) critical for AI accelerators. Any shift in the market's assessment of AI capex sustainability, Nvidia's financing posture, or Chinese competitive pressure flows directly into these stocks' earnings expectations. A 13.4% single-session decline in Samsung is not a sentiment wobble; it reflects a rapid repricing of forward estimates.

The timing ahead of Big Tech earnings compounds the uncertainty. If those earnings confirm AI capex deceleration, the repricing that hit Samsung and SK Hynix on July 28 becomes a leading indicator rather than an overreaction. If earnings disappoint on the upside, the gap between today's prices and revised expectations will need to close. Either way, the market has moved from pricing AI growth as a one-directional trade to pricing it as a risk event.

For investors and allocators, the key data points are straightforward: KOSPI down more than 8%, circuit breaker triggered, Samsung down 13.4%, SK Hynix down 10%, Nikkei down 4.3% at 62,127.57, Taiex down 3.9%. The catalyst cluster is AI-sector-specific: Nvidia financing concerns, China competition, and Big Tech earnings event risk. Whether this proves a flush or a trend reversal depends on the earnings prints ahead, but the positioning unwind has already done its damage.