South Korea’s benchmark KOSPI index has whipsawed through one of the most volatile stretches in its history over the past several weeks, swinging between historic single-day losses and record-setting rebounds as investors struggle to settle on a consistent view of the country’s chip-heavy stock market. Here is a breakdown of the key factors driving that turbulence.

1. Extreme concentration in just two chip stocks

Samsung Electronics and SK Hynix together account for more than half of the KOSPI’s total market weighting, a level of concentration that has effectively turned the entire benchmark index into a direct proxy for global sentiment toward artificial intelligence hardware spending. When either company’s shares move sharply, whether up or down, the effect ripples through the headline index with far greater force than a comparably diversified market would experience. That dynamic has meant that daily earnings reactions, competitive news or supply announcements involving either company can single-handedly swing the KOSPI by several percentage points in a single session.

2. Whiplash reactions to memory chip earnings

Both companies’ recent earnings reports have triggered dramatically different market reactions depending on how results compared with elevated investor expectations, rather than the underlying strength of the results themselves. SK Hynix reported a sixfold increase in operating profit and record revenue, yet shares initially fell sharply because the figures still came in below the loftier expectations investors had built around AI-related chip demand. Samsung’s semiconductor division separately reported operating income more than 250 times higher than the prior year, a result that, combined with other catalysts, helped fuel one of the sharpest single-day rallies in KOSPI history.

3. Intensifying competition from Chinese chipmakers

Growing concerns about Chinese memory chip manufacturers narrowing the technological gap with South Korean producers have added a structural layer of anxiety to the recent volatility. The successful stock market debut of Chinese memory chip manufacturer CXMT, along with reports that Chinese firms have made progress developing advanced deep ultraviolet lithography equipment, has repeatedly weighed on sentiment toward Samsung and SK Hynix, since both companies face the prospect of lower-cost Chinese rivals eventually competing for market share in the global memory chip industry.

4. Broader doubts about AI infrastructure spending sustainability

The KOSPI’s swings have closely tracked a broader global reassessment of whether massive capital spending on artificial intelligence infrastructure can continue at its current pace. Selloffs in Korean chip stocks have repeatedly coincided with steep declines in U.S. semiconductor names, driven in part by investor concerns about unusually large, circular financing arrangements between major AI infrastructure providers and their customers. Conversely, the KOSPI’s most dramatic rebound to date came directly on the heels of blockbuster earnings from Microsoft, Amazon and Meta Platforms, which eased those same concerns and sent chip stocks surging across Asian markets overnight.

5. Leveraged trading and mechanical market structure

Elevated participation by individual investors in leveraged exchange-traded funds tracking the semiconductor sector has repeatedly amplified volatility in both directions throughout the recent turbulence. When the KOSPI or the smaller KOSDAQ index falls or rises 8% or more within a single session, automatic circuit breakers and “sidecar” mechanisms designed to halt trading or suspend program orders have been triggered on multiple occasions in recent weeks, at times on both the KOSPI and KOSDAQ on consecutive trading days for the first time in the exchange’s history. New cash-deposit requirements for leveraged ETF investors, which took effect July 31, were specifically introduced by regulators in an effort to reduce this kind of mechanically amplified volatility going forward.

6. Shifting foreign investor flows

Foreign investor activity has swung sharply during the recent turmoil, adding another layer of instability to the index. During the sharpest phase of the selloff, foreign investors sold tens of trillions of won worth of Korean stocks over consecutive weeks. That pattern reversed abruptly during the KOSPI’s record rebound session, when foreign investors posted net purchases exceeding 7 trillion won in a single day, marking a second consecutive session of net foreign buying after four straight sessions of net selling beforehand. Institutional investors have shown a similarly inconsistent pattern, at times reversing from net sellers to net buyers within the same trading session.

The scale of the recent swings has been extraordinary by historical standards. The KOSPI plunged more than 17% over three trading sessions in late July, at one point falling roughly 40% from its June peak and wiping out nearly $2 trillion in market value, before rebounding with a single-day gain of 17.91%, the largest in the index’s history, a move that still left the KOSPI down 22.19% for the month of July overall, its worst monthly performance since 1997.

Market analysts have urged caution about reading too much into any single day’s move given the scale of the recent volatility. One analyst, speaking to CNBC following the record rebound session, cautioned that asset prices had become “completely disconnected” from underlying fundamentals during the recent turmoil, adding, “I would not expect gains of this magnitude to continue.”

South Korean authorities have moved to address the broader instability directly, announcing plans to inject at least 20 trillion won into the Korea Investment Corporation for strategic investments in artificial intelligence, data centers and broader infrastructure, marking the first time the sovereign wealth fund’s mandate has been expanded to include domestic assets. With the structural drivers behind the recent volatility, chip stock concentration, AI spending uncertainty, Chinese competition and leveraged trading dynamics, still largely unresolved, analysts expect the KOSPI to remain unusually sensitive to incoming earnings, geopolitical developments and shifts in global technology sector sentiment in the weeks ahead.