KOSPI closed at 5,663.24 on July 29, down 360.42 points, or 5.98% [E6]. That official settlement is severe enough without importing a deeper intraday print from a blocked wire page. Portfolios and policy books carry the close, while trading halts carry the image of collapse. Two stocks sitting at the center of the benchmark and the retail leverage trade delivered the break [E3].
By July 15, Samsung Electronics and SK hynix together represented 52% of KOSPI, up from 34% at the end of 2025 [E3]. Domestic single-stock leveraged products tied to the same pair had grown from ₩4.4 trillion at launch to ₩11.9 trillion in less than two months [E3]. The rules allowed 200% exposure, turning one-day stock moves into a 2x retail product [E1]. Launch guidance had already warned that Korea’s ±30% stock limit could translate into a 60% one-day loss for the wrapper [E2].
SK hynix supplied the spark by reporting record second-quarter revenue of ₩79.3187 trillion and record operating profit of ₩60.5426 trillion [E5]. The company also pointed to long-term agreements with about 10 key customers and continued strength in AI demand [E5]. Record accounts landing on a 5.98% KOSPI down day show that investors had budgeted for an even cleaner AI-memory path [E5][E6]. The break reads as an expectations reset transmitted through an unusually concentrated market structure [E3][E5][E6].
A daily 2x long product must restore its target exposure after the underlying moves [E1]. After a sharp fall, its remaining exposure can exceed twice the smaller net asset value, forcing the fund or its hedge provider to cut exposure into weakness. When several products reset around the same two names, selling can bunch near the rebalance window and feed back into price discovery. With those names at 52% of KOSPI, a local hedge adjustment can quickly become an index-level event [E1][E3].
Regulators had started tightening the machine before the earnings shock reached the index [E3][E4]. On July 16, the Financial Services Commission suspended new listings and advertising while product capitalization was already at ₩11.9 trillion [E3]. On July 24, it moved the entry deposit to ₩30 million in cash from July 31 [E4]. After the July 29 break, the finance ministry convened an emergency market review; its accessible page confirms the meeting while the attachment’s precise rules and start dates remain unresolved [E7].
The null case is brutally simple: half an index in two chipmakers will look systemic whenever the AI-memory valuation breaks. Samsung and SK hynix alone supplied 52% of KOSPI’s market weight before the selloff [E3]. SK hynix’s record operating result shows that repricing can begin in expectations even while the company prints exceptional profits [E5]. No public fund-by-fund ledger shows the July 29 rebalance orders, so the products qualify as a plausible accelerant while their share of the bill remains unpriced [E3][E6].
Policy now forces retail capital to carry more cash, accept lower concentration and pay more friction before chasing the same two names [E4][E7]. That may shrink the leverage aisle, yet it cannot diversify KOSPI overnight. Every earnings release from Icheon still lands inside a benchmark where Samsung and SK hynix together held 52% [E3]. Korea built a two-stock leverage machine on the same axle that carried half the market; the next disappointment will still arrive with the index aboard.