On July 2, the Kospi fell 7.89 percent to 7,648.09. SK Hynix dropped 14.57 percent. Samsung Electronics fell 9.06 percent. The Korea Exchange activated a sell-side sidecar on Kospi 200 futures when they fell more than 5 percent, then triggered a full circuit breaker after the index declined past 8 percent. It was the fourth circuit breaker of 2026. Foreign investors were net sellers of more than 4 trillion won.
The trigger was an announcement from Menlo Park. On July 1, Meta disclosed a cloud business called Meta Compute that will lease idle data center capacity to outside clients. Meta's stock rose more than 7 percent, adding more than $100 billion in market capitalization. The operative disclosure was not the product. It was the word idle. The company had built more AI infrastructure than it needed. The scarcity premium that had justified semiconductor valuations since 2024 evaporated in a single filing.
The repricing moved through the supply chain in sequence. The Philadelphia Semiconductor Index fell 6.27 percent. Micron dropped more than 10 percent. CoreWeave fell more than 10 percent. Nebius dropped more than 12 percent. Then it crossed the Pacific. SK Hynix controls approximately 60 percent of the world's High Bandwidth Memory, the stacked DRAM packaged beside every AI accelerator. If Meta has surplus compute, the forward demand curve for HBM shifts. Samsung and SK Hynix together represent approximately 60 percent of the Kospi. When two companies are 60 percent of a national stock exchange, a revision in their demand outlook is not a sector rotation. It is a market event.
Goldman Sachs had warned that each additional percentage point of concentration by the two chipmakers could trigger approximately $2 billion in forced selling by foreign institutions bound by US Investment Company Act diversification rules. On July 2, foreign investors dumped Korean equities at a pace that exceeded even the Goldman scenario. The concentration did not cause the crash through the specific regulatory channel Goldman described. It produced the same result through a different channel: a decline concentrated enough to activate circuit breakers designed for market-wide emergencies, triggered by two stocks in one industry.
Days before the crash, SK Hynix had filed for the largest ADR offering in history. The $29 billion Nasdaq listing was designed to escape exactly this fragility. The filing argued, in the language of capital markets, that SK Hynix had outgrown the Korean exchange. The crash made the argument in plainer terms. A single American company's product announcement, twelve hours and eight thousand miles away, sent the Korean national index past the circuit breaker threshold.
A sidecar, in Korean exchange terminology, is a temporary halt on index futures trading when derivatives fall too fast. The word also describes a vehicle that cannot steer. It goes wherever the motorcycle goes. The Kospi has become a sidecar to American AI capital expenditure decisions. When American companies build AI infrastructure, Korean chipmakers rise. When one announces it has built more than it needs, the Korean national index triggers the mechanism named for the thing it has become.