KOSPI Plunges 8% as SK Hynix and Samsung Lead Chip Sell-Off

South Korean Stocks Trigger Market-Wide Circuit Breaker

South Korea’s stock market suffered another period of extreme volatility on Monday as the KOSPI fell more than 8% during afternoon trading, forcing the Korea Exchange to activate a market-wide circuit breaker.

The benchmark’s decline reportedly reached 8.07%, taking it below the psychologically important 7,000 level. The index touched approximately 6,880 at its intraday low, representing its weakest point in about two months.

Trading was suspended for 20 minutes at around 1:28 p.m. Seoul time after the index reached the circuit-breaker threshold. The interruption was intended to give investors time to assess conditions during a rapid and disorderly market move.

The figures represented intraday levels rather than confirmed closing prices, meaning the final scale of the session’s decline could differ after trading resumed.

The sell-off was concentrated in South Korea’s largest semiconductor companies. SK Hynix and Samsung Electronics together account for an unusually large share of the KOSPI’s market capitalisation, making sharp movements in the two stocks particularly influential for the broader index.

SK Hynix Reverses Gains After Strong Nasdaq Debut

SK Hynix emerged as one of the largest contributors to Monday’s decline. Its Seoul-listed shares fell more than 14% intraday to approximately KRW 1.876 million, extending their retreat below the KRW 2 million level and reaching their lowest point since early June.

The decline contrasted sharply with the reception for the company’s American Depositary Receipts on Nasdaq. SK Hynix’s ADRs, trading under the SKHY ticker, rose 12.8% during their first US session after being priced at $149 and opening at $170. The company raised more than $26 billion through the transaction. Reuters

However, a successful US debut did not eliminate the risk of profit-taking in Seoul. SK Hynix shares had already recorded substantial gains during the AI-memory rally, leaving the stock sensitive to changes in earnings expectations and investor positioning.

Early in Monday’s session, Reuters attributed part of the decline to profit-taking and more cautious expectations for HBM4 shipment growth. Investors are assessing whether near-term shipments can meet the optimistic assumptions reflected in semiconductor valuations.

This distinction is important. The long-term case for high-bandwidth memory remains linked to expanding AI infrastructure investment, but share prices may still fall when reported shipments, margins or production guidance fail to exceed elevated market expectations.

Samsung Electronics Adds to Pressure on the KOSPI

Samsung Electronics also came under heavy selling pressure, falling more than 10% intraday to around KRW 255,500. That placed the stock near its lowest level since early May.

As another major KOSPI constituent, Samsung’s decline added considerably to the benchmark’s losses. The simultaneous retreat in Samsung and SK Hynix meant that weakness was concentrated in the two companies most closely associated with South Korea’s AI and memory-chip rally.

Samsung has a broader business portfolio than SK Hynix, spanning memory chips, foundry services, consumer electronics and smartphones. Nevertheless, its share price remains highly sensitive to changes in memory-chip pricing and expectations for AI-related semiconductor demand.

The company is also accelerating its long-term semiconductor investment. Samsung plans to bring forward the opening of a new Yongin chip fabrication facility to 2029 as South Korea seeks to expand domestic production capacity in response to AI-related memory demand. Reuters

These investment plans support the industry’s longer-term production outlook, but they also raise questions about capital expenditure, future supply growth and the risk of overcapacity if AI infrastructure spending slows.

Middle East Conflict Intensifies Risk-Off Sentiment

The semiconductor decline unfolded alongside renewed geopolitical tension in the Middle East. US and Iranian forces exchanged further strikes over the weekend, while uncertainty surrounding commercial passage through the Strait of Hormuz increased.

Shipping activity through the strait fell to a five-week low on Sunday, according to ship-tracking data cited by Reuters. The renewed hostilities also pushed Brent and WTI crude prices more than 4% higher, reviving concerns about energy costs and global inflation. Reuters

South Korea is particularly exposed to energy-market disruptions because it depends heavily on imported oil and gas. A sustained increase in crude prices could weaken its trade balance, increase costs for manufacturers and complicate the inflation outlook.

Higher energy prices may also affect expectations for global monetary policy. If the oil shock proves persistent, central banks could face greater difficulty easing interest rates, creating an additional challenge for highly valued technology and semiconductor stocks.

However, geopolitical escalation should not be treated as the sole cause of the KOSPI decline. The market was already experiencing substantial volatility due to semiconductor concentration, profit-taking and changing expectations for the AI investment cycle.

Semiconductor Concentration Amplifies Market Volatility

The latest sell-off highlights the KOSPI’s increasing dependence on a small number of semiconductor companies. When SK Hynix and Samsung rise together, their combined market weight can drive the index sharply higher. The same concentration works in reverse during a downturn.

Leveraged single-stock exchange-traded products may further magnify these movements. South Korean regulators have recently raised concerns that products offering amplified exposure to individual chipmakers can intensify one-way trading during periods of stress.

A decline in the underlying shares can force leveraged products to rebalance their holdings, potentially adding to late-session selling pressure. This does not mean leveraged ETFs caused Monday’s decline, but their growing presence may have increased the market’s sensitivity to sudden changes in sentiment.

The KOSPI had already fallen more than 20% from its June record close before Monday’s deeper slide, although it remained one of the strongest-performing major global benchmarks of 2026.

What Traders Should Watch Next

The immediate outlook will depend partly on whether the KOSPI stabilises after trading resumes and whether SK Hynix and Samsung recover from their intraday lows.

Investors will also monitor the relative performance of SK Hynix’s Seoul shares and Nasdaq ADRs. A large or persistent price difference could generate arbitrage activity, although currency movements, depositary ratios and local trading restrictions must be considered when comparing the two securities.

Upcoming semiconductor earnings will provide a more fundamental test. Guidance from SK Hynix, Samsung, TSMC and ASML could clarify whether AI-related chip demand remains strong enough to support current capacity expansion and valuation assumptions.

Geopolitical developments around the Strait of Hormuz remain another important variable. A further reduction in shipping traffic could keep oil prices elevated and reinforce risk aversion. Conversely, credible de-escalation could reduce pressure on energy-importing markets such as South Korea.

For now, Monday’s move reflects a combination of geopolitical risk and domestic market structure. Strong long-term demand for AI memory does not remove the possibility of sharp corrections, particularly when positioning, valuations and index concentration are already elevated.