Author: Shenchao TechFlow
At 9:03:42 AM on June 8, the main board of the Korean exchange triggered a Level 1 circuit breaker.
With only 3 minutes and 42 seconds remaining until market open, the KOSPI has dropped from the previous trading day’s closing price of 8,160.59 to 7,477.46, a single-day decline of 8.37%. Under Korean regulations, a Level 1 circuit breaker is triggered when the index falls more than 8% from the previous day’s closing price and remains below that threshold for over one minute, resulting in a 20-minute halt of trading on the main board.
KOSDAQ plunged over 7%, triggering a circuit breaker mechanism for programmatic selling. Selling pressure was heavily concentrated on large-cap stocks: Samsung Electronics fell 10% intraday, breaking below the 300,000 KRW threshold; SK Hynix dropped 10% intraday, falling below the 2,000,000 KRW mark; and other major constituents such as Hyundai Motor and LG Electronics also posted near double-digit declines. Foreign investors net sold 342.1 billion KRW in KOSPI stocks during the morning session.
Samsung and SK Hynix account for half of the market capitalization and contribute approximately 70% of the KOSPI's year-to-date gains.
The 2026 gains in the Korean stock market were primarily driven by two stocks.
According to Goldman Sachs data cited by CryptoRank, Samsung Electronics and SK Hynix together account for more than half of the KOSPI’s total market capitalization and contribute approximately 70% of the index’s gains since the beginning of 2026. Driven by these two stocks, the KOSPI’s year-to-date gain once surpassed 90%, with its total market capitalization swelling to around $5 trillion, surpassing Canada, Germany, the UK, and France to become the world’s sixth-largest stock market.
The breadth of the bull market falls far short of its depth. According to statistics cited by Sina Finance, as of the end of May 2026, the KOSPI comprised 835 listed companies; under the 2026 bull market, only 373 stocks rose, fewer than half. Excluding the two semiconductor giants, the remaining 800+ stocks contributed less than 30% to the index’s gain.
This market-called "K-shaped divergence" has determined a simple fact: when Samsung and SK Hynix are sold off simultaneously, the KOSPI has no buffer. The cost of this structural concentration was evident in the minutes following the open on June 8.
Broadcom's guidance became the trigger, causing a cross-market selling chain to spread to Seoul overnight.
The trigger for this selling spree came from U.S. semiconductor stocks.
After hours on June 3, Broadcom reported its second-quarter fiscal year 2026 results. Absolute figures hit record levels: revenue reached $22.19 billion, up 48% year-over-year, with AI semiconductor revenue at $10.8 billion, up 143% year-over-year. However, the market focused on Broadcom’s Q3 FY2026 AI chip revenue guidance of $16 billion, which fell short of the LSEG consensus sell-side estimate of $17.2 billion by approximately $1.2 billion, or about 7%. In its SEC 8-K filing, Broadcom CEO Hock Tan confirmed, “For Q3, we expect AI semiconductor revenue to grow more than 200% year-over-year to $16 billion,” and maintained its full-year AI semiconductor revenue guidance at $56 billion without an increase.
The market interpreted the "no increase" decision extremely negatively. Broadcom's stock fell 14% that day, and Micron dropped 7%. On Friday last week, all three major U.S. stock indices plunged simultaneously: the Dow fell 1.35%, the S&P 500 dropped 2.64%—its largest single-day decline since October 2025—and the Nasdaq slid 4.18%, marking its biggest one-day loss since April 2025; the Philadelphia Semiconductor Index (SOX) tumbled 10.26%, its largest single-day decline since the March 2020 COVID-19 shock.
The selling pressure spread to South Korea last Friday. On June 5, the KOSPI fell 5.54% to close at 8,160.59, triggering its 10th circuit breaker suspension of the year. Samsung Electronics dropped 6.4% to KRW 329,000, while SK Hynix slid 9.92% to KRW 2,070,000. Foreign investors net sold KRW 352 billion, and institutional investors net sold KRW 939.9 billion, making retail investors the only net buyers, purchasing KRW 422 billion. Foreign selling has now continued for 20 consecutive trading days, with cumulative net outflows reaching KRW 7 trillion.
The KOSPI night session futures closed last Friday at the 8% lower circuit limit, setting a price channel for the crash-like decline that occurred after opening on June 8.
38 trillion KRW margin loans combined with leveraged ETFs accelerate mechanical selling.
If foreign capital's continuous selling represents visible pressure, retail investors' hidden leverage is the structural amplifier behind this circuit breaker.
According to data from the Korea Financial Investment Association, South Korean retail investors' margin loan balances reached a record high of KRW 3.802 trillion as of May 29; they remained at a high level of KRW 3.774 trillion as of June 4.
Mechanical selling stems from three levels. The first is forced liquidation. When Samsung and SK Hynix each fell 10% in a single day, leveraged accounts hit their margin call thresholds, compelling brokers to sell collateralized securities. On June 8, one of South Korea’s leading brokers, Korea Investment & Securities, announced a suspension of margin trading, citing exhausted credit limits.
The second layer comes from 2x leveraged ETFs on single stocks. This year, South Korea’s market introduced new 2x leveraged ETF products linked to Samsung Electronics and SK Hynix. When the underlying stocks decline, these ETFs must sell the corresponding shares at a 2x ratio to maintain their leveraged positions—the faster the decline, the more urgent the selling.
The third layer is algorithmic trading. After a decline in KOSPI 200 futures triggers the algorithmic trading halt mechanism, algorithmic trading is paused for five minutes; however, once the pause period ends, quantitative strategies such as CTA continue to reduce positions proportionally according to their predefined models.
The Korean won is under synchronized pressure. According to TradingKey and EBC, the won has fallen to around 1,560 against the U.S. dollar, marking its weakest level since the global financial crisis in 2009. On Friday, the won closed at 1,539.1 per dollar, having briefly approached 1,550 during the session—it has now traded above 1,500 per dollar for 14 consecutive trading days. The won’s depreciation is accelerating capital outflows, creating a negative feedback loop: “sell stocks, buy dollars, won depreciates further, prompting more foreign capital to exit.”
Regulators have urgently intervened, validating the warning issued by the central bank governor a week ago.
South Korean authorities have begun issuing statements. On the morning of June 8, South Korea’s Minister of Finance, together with the Bank of Korea and financial regulators, released an emergency statement pledging to “take immediate action as needed to address excessive market volatility” and warning of leverage risks. This marks the highest-level coordinated statement from South Korean authorities since multiple circuit breakers were triggered earlier this year.
More worth reflecting on is the warning issued a week ago by Bank of Korea Governor Rhee Chang-yong. At a press conference following the Monetary Policy Committee meeting on May 28, Rhee stated, “At this point, we do not believe that debt-financed investment will escalate into a systemic risk,” but he immediately added, “If debt-driven investment becomes widespread, even those who have not borrowed to invest could suffer corresponding losses if a small shock triggers a significant market adjustment.”
This warning came less than two weeks after the circuit breaker on June 8.
Institutional sentiment toward the KOSPI remains unchanged in the long term. According to CryptoRank, Goldman Sachs maintains its 12-month target of 12,000 points for the KOSPI, implying approximately 60% upside potential even from the intraday low of 7,477 points.
But the crash on June 8 revealed a fact masked by the frenzy: when the story of the "two giants" began to lose its luster, the two pillars that drove a 90% rally could also wipe out 8.37% of the index in a single day.