Author: Deep Tide TechFlow

On June 8 at 9:03:42 AM, the main board of the Korea Exchange triggered a Level 1 circuit breaker.

At this time, only 3 minutes and 42 seconds had passed since the market opened, and the KOSPI had dropped from the previous trading day's closing price of 8160.59 to 7477.46, a single-day decline of 8.37%. According to Korean regulations, when the index drops more than 8% compared to the previous trading day's closing price and continues for more than 1 minute, a Level 1 circuit breaker is activated, pausing trading on the main board for 20 minutes.

KOSDAQ simultaneously plummeted over 7%, triggering the selling side of the programmatic trading suspension mechanism. The sell-off was highly concentrated in large-cap stocks, with Samsung Electronics dropping 10% during trading, falling below the 300,000 won mark; SK Hynix also fell 10%, dropping below the 2,000,000 won mark; other heavyweight stocks such as Hyundai Motor and LG Electronics also saw close to double-digit declines. In the early session, foreign investors net sold KOSPI stocks for 342.1 billion won.

Samsung+ SK Hynix account for half of the market value, contributing about 70% of KOSPI's annual rise

The rise of the Korean stock market in 2026 was mainly driven by two stocks.

According to Goldman Sachs data quoted by CryptoRank, Samsung Electronics and SK Hynix together account for more than half of KOSPI's total market value, contributing about 70% of the index's increase from the beginning of 2026 to the present. With the pull from these two stocks, the KOSPI's rise since the beginning of the year once exceeded 90%, with a total market value swelling to about 50 trillion dollars, surpassing Canada, Germany, the UK, and France to become the sixth largest stock market in the world.

The breadth of the bull market is far less than its depth. According to statistics quoted by Sina Finance, as of the end of May 2026, there were a total of 835 listed companies on the KOSPI, but only 373 stocks rose during the bull market in 2026, less than half; excluding the two chip giants, the remaining over 800 stocks contributed less than 30% to the index's rise.

This phenomenon, referred to as "K-shaped divergence" by the market, determines a simple fact: when both Samsung and SK Hynix are sold off simultaneously, there is no buffer for the KOSPI. A few minutes after the opening on June 8, the price of this structural concentration became apparent.

Broadcom's guidance became the fuse, and the cross-market sell-off transmitted overnight to Seoul

The trigger for this round of selling came from U.S. semiconductor stocks.

On June 3 after the U.S. stock market closed, Broadcom released its second quarter results for fiscal year 2026. Absolute figures set a record, with revenue of 22.19 billion dollars, a year-on-year increase of 48%, and AI semiconductor revenue of 10.8 billion dollars, a year-on-year increase of 143%. However, the market focused on the Q3 FY2026 AI chip revenue guidance, which was 16 billion dollars, below the consensus expectation of 17.2 billion dollars from LSEG by about 1.2 billion dollars, a gap of about 7%. Broadcom CEO Hock Tan confirmed in the SEC 8-K filing that "we expect AI semiconductor revenue in Q3 to year-on-year increase over 200% to 16 billion dollars," and maintained the full-year AI semiconductor revenue guidance of 56 billion dollars without an upward adjustment.

The market interpreted the "no upward adjustment" very negatively. Broadcom's stock price fell 14% that day, while Micron fell 7%. Last Friday, the three major U.S. stock indexes all fell sharply, with the Dow Jones down 1.35%, the S&P 500 down 2.64%, marking the largest single-day drop since October 2025, and the Nasdaq down 4.18%, the largest single-day drop since April 2025; the Philadelphia Semiconductor Index (SOX) plummeted 10.26% in a single day, the largest daily drop since the onset of the COVID-19 pandemic in March 2020.

The sell-off chain was transmitted to Korea last Friday. On June 5, the KOSPI fell 5.54% to close at 8160.59, triggering the programmatic trading suspension mechanism for the 10th time this year during the session. Samsung Electronics fell 6.4% to 329,000 won, while SK Hynix fell 9.92% to 2,070,000 won. On that day, foreign investors net sold 35.2 trillion won, institutional investors net sold 939.9 billion won, while retail investors were the only net buyers, net buying 42.2 trillion won. Foreign selling had continued for 20 trading days, with a cumulative net outflow of 70 trillion won.

The KOSPI night futures closed last Friday at the 8% limit down price, setting the stage for the collapse-style drop after the opening on June 8.

38 trillion won margin loans combined with leveraged ETFs accelerated mechanical selling

If the continuous foreign selling is the explicit pressure, the implicit leverage of retail investors is the structural amplifier of this circuit breaker.

According to data from the Korea Financial Investment Association, the balance of credit financing (margin loans) for retail investors in Korea reached 38.02 trillion won as of May 29, a historic high; it remained at a high level of 37.74 trillion won as of June 4.

The mechanical sell-off comes from three levels. The first level is forced liquidation. When Samsung and SK Hynix fall 10% in a single day, leveraged accounts hit the forced liquidation line, and brokers must sell the collateralized securities. On June 8, one of Korea's leading brokerages, Korea Investment & Securities, announced a suspension of margin trading on the grounds that credit limits had been exhausted.

The second level comes from single-stock 2x leveraged ETFs. This year, the Korean market has introduced 2x leveraged ETF products linked to Samsung Electronics and SK Hynix. When the underlying stocks decline, these ETFs must sell the corresponding stocks at a 2x ratio to maintain their leveraged positions; the faster the decline, the more urgent the selling.

The third level is programmatic trading. When the KOSPI200 futures trigger the programmatic suspension mechanism due to a drop, programmatic trading is paused for 5 minutes, but after the pause ends, strategies like CTA continue to reduce positions proportionally according to established models.

The won is also under pressure. According to reports from TradingKey and EBC, the won against the dollar has fallen to around 1560, the weakest range since the global financial crisis in 2009. Last Friday, the won closed at 1539.1/USD, at one point approaching 1550, having run above 1500/USD for 14 consecutive trading days. The depreciation of the won further accelerated the outflow of foreign capital, creating a negative feedback loop of "sell stocks, exchange for dollars, won depreciation, more foreign selling."

Regulators intervene urgently, Central Bank Governor's warning a week ago proves to be prescient

The Korean authorities began to speak out. On the morning of June 8, the Korean Minister of Finance, in conjunction with the Central Bank (Bank of Korea) and financial regulatory authorities, issued an urgent statement promising to "take immediate action to respond to excessive market volatility as necessary," and warned of leverage risks. This was the highest-level joint statement from the Korean authorities since multiple circuit breakers this year.

What is worth revisiting is the warning by Bank of Korea Governor Rhee Chang-yong a week ago. At a press conference following the monetary policy committee meeting on May 28, Rhee stated, "At present, we do not believe that debt-financed investments will escalate into systemic risks," but he immediately added, "If debt-driven investments become widespread, a small shock could lead to a significant market adjustment, and those who have not borrowed to invest may also suffer corresponding losses."

This warning came less than two weeks before the circuit breaker on June 8.

Institutions' long-term judgment on the KOSPI has not yet shifted. According to CryptoRank, Goldman Sachs maintains a 12-month target price of 12,000 points for the KOSPI, implying that even starting from the intraday low of 7,477 points, Goldman still expects about a 60% upside potential.

However, the sharp decline on June 8 highlighted a fact obscured by the frenzied market: when the story of the "duo" starts to discount, the two pillars that supported a 90% rise can also take away 8.37% of the index in a single day.