Author: Deep Tide TechFlow
At 9:03:42 AM on June 8, a first-tier circuit breaker was triggered on the main board of the Korea Exchange.
Just 3 minutes and 42 seconds after the opening, the KOSPI had dropped from the previous trading day's close of 8160.59 to 7477.46, a single-day decline of 8.37%. According to Korean rules, when the index falls more than 8% compared to the previous day's close and the decline persists for over 1 minute, a first-tier circuit breaker is activated, halting trading on the main board for 20 minutes.
The KOSDAQ also plunged over 7%, triggering the mechanism to suspend sell-side program trading. Selling was heavily concentrated in large-cap stocks: Samsung Electronics fell by 10% intraday, breaking below the 300,000 won mark; SK Hynix fell by 10% intraday, breaking below the 2,000,000 won mark; other heavyweight stocks like Hyundai Motor and LG Electronics also saw declines nearing double digits. In the morning session, foreign investors net sold 3,421 billion won worth of KOSPI stocks.
Samsung + SK Hynix Account for Half the Market Cap, Contribute ~70% of KOSPI's Year-to-Date Gains
The gains in the South Korean stock market in 2026 have been driven primarily by two stocks.
According to Goldman Sachs data cited by CryptoRank, Samsung Electronics and SK Hynix together account for over half of the KOSPI's total market capitalization and contributed approximately 70% of the index's year-to-date gains in 2026. Pulled by these two stocks, the KOSPI's year-to-date gains once exceeded 90%, and its total market capitalization swelled to around $5 trillion, successively surpassing Canada, Germany, the UK, and France to become the world's sixth-largest stock market.
The breadth of the bull market is far less impressive than its depth. Statistics cited by Sina Finance show that as of the end of May 2026, there were 835 listed companies on the KOSPI. Despite the 2026 bull market, only 373 stocks rose, less than half. Excluding the two chip giants, the remaining 800+ stocks contributed less than 30% to the index's gains.
This market structure, referred to as a "K-shaped divergence," determined a simple fact: when Samsung and SK Hynix are sold off simultaneously, the KOSPI has no buffer. The minutes following the opening on June 8 were the price paid for this structural concentration.
Broadcom's Guidance Became the Trigger, Cross-Market Selling Chain Overnight Transmitted to Seoul
The trigger for this round of selling came from U.S. semiconductor stocks.
After the U.S. market closed on June 3, Broadcom released its fiscal 2026 second-quarter results. The absolute figures were record-breaking: revenue of $22.19 billion, up 48% year-over-year, with AI semiconductor revenue of $10.8 billion, up 143% year-over-year. However, the market focused on the Q3 FY2026 AI chip revenue guidance of $16 billion, which was about $1.2 billion (approximately 7%) below the sell-side consensus expectation of $17.2 billion compiled by LSEG. In an SEC 8-K filing, Broadcom CEO Hock Tan confirmed, "In Q3, we expect AI semiconductor revenue to grow over 200% year-over-year to $16 billion," and maintained the full-year AI semiconductor revenue guidance of $56 billion, without raising it.
The market interpreted the "lack of an upward revision" extremely negatively. Broadcom's stock fell 14% that day; Micron fell 7%. Last Friday, the three major U.S. stock indices slumped simultaneously: the Dow fell 1.35%, the S&P 500 fell 2.64% (its largest single-day drop since October 2025), and the Nasdaq fell 4.18% (its largest single-day drop since April 2025); the Philadelphia Semiconductor Index (SOX) plunged 10.26%, its largest single-day drop since the COVID-19 shock in March 2020.
The selling chain had already been transmitted to South Korea last Friday. On June 5, the KOSPI fell 5.54% to close at 8160.59, triggering the year's 10th program trading suspension mechanism intraday. Samsung Electronics fell 6.4% to 329,000 won; SK Hynix fell 9.92% to 2,070,000 won. That day, foreign investors net sold 3.52 trillion won, institutions net sold 939.9 billion won, leaving retail investors as the sole net buyers, net purchasing 4.22 trillion won. Foreign selling has persisted for 20 consecutive trading days, with cumulative net outflows reaching 70 trillion won.
The KOSPI night futures closed at the 8% limit-down price last Friday, setting the price channel for the crash-like decline after the opening on June 8.
38 Trillion Won in Margin Loans Coupled with Leveraged ETFs, Mechanical Selling Accelerates
If the continuous selling by foreign investors was the visible pressure, the hidden leverage of retail investors acted as the structural amplifier for this circuit breaker.
According to data from the Korea Financial Investment Association, South Korean retail credit financing balances (margin loans) reached a record high of 38.02 trillion won as of May 29; as of June 4, they remained elevated at 37.74 trillion won.
Mechanical selling came from three layers. The first layer is forced liquidation. When Samsung and SK Hynix fall 10% in a day, leveraged accounts hit forced liquidation lines, requiring brokers to sell the pledged securities. On June 8, Korea Investment & Securities, one of South Korea's leading brokerages, announced the suspension of margin trading, citing depleted credit limits.
The second layer came from single-stock 2x leveraged ETFs. This year, 2x leveraged ETF products linked to Samsung Electronics and SK Hynix were newly launched in the South Korean market. When the underlying stocks fall, such ETFs must sell the corresponding stocks at twice the rate to maintain their leveraged positions. The faster the decline, the more urgent the selling.
The third layer is program trading. After the KOSPI200 futures decline triggered the program trading suspension mechanism, program trading halted for 5 minutes. However, after the suspension period ended, quantitative strategies like CTAs continued to reduce positions proportionally according to their predetermined models.
The Korean won also came under simultaneous pressure. According to reports from TradingKey and EBC, the won has fallen to around 1560 against the U.S. dollar, its weakest level since the 2009 global financial crisis. Last Friday, the won closed at 1539.1 per dollar, having briefly approached 1550 intraday, marking 14 consecutive trading days above 1500 per dollar. The won's depreciation further accelerated foreign capital outflows, creating a negative feedback loop of "sell stocks, exchange for dollars, won depreciates, more foreign selling."
Regulators Rush to Intervene, Central Bank Governor's Warning from a Week Ago Comes True Early
South Korean authorities began issuing statements. On the morning of June 8, the South Korean Finance Minister, jointly with the central bank (Bank of Korea) and financial regulators, issued an emergency statement promising to "take immediate action as necessary to address excessive market volatility" and warned of leverage risks. This is the highest-level joint statement from South Korean authorities since the multiple circuit breakers this year.
More noteworthy for review is the warning from Bank of Korea Governor Rhee Chang-yong a week earlier. At a press conference following the Monetary Policy Committee meeting on May 28, Rhee stated, "We don't think debt-financed investment will escalate into a systemic risk at this point." However, he immediately added: "If debt-driven investment becomes widespread, a small shock leading to a significant market adjustment could also cause losses for those who did not invest with borrowed money."
This warning came less than two weeks before the June 8 circuit breaker.
Institutions have not yet shifted their long-term outlook on the KOSPI. According to CryptoRank, Goldman Sachs maintains its 12-month target for the KOSPI at 12,000 points, implying an expected upside of approximately 60% even from the intraday low of 7,477 points.
But the June 8 plunge highlights a fact obscured by the frenzied rally: when the story of the "two titans" starts to get discounted, the two pillars that propped up 90% of the gains can also wipe out 8.37% of the index in a single day.
