A single-day plunge of nearly 10% triggers four circuit breakers, a stock market stampede disaster built on nationwide leverage.

The most explosive event in recent capital markets has to be the normalization of South Korea's stock market circuit breakers: KOSPI plummeted 9.99% in a single day, triggering a full-market trading halt, with four circuit breakers in a year setting a historical record. Samsung and SK Hynix plunged over 12%, trillions in leveraged positions were liquidated in a chain reaction, foreign capital fled en masse, and retail investors saw trillions in bottom-fishing funds trapped. This crash was no accident—it was a textbook stock market disaster triggered by a combination of industrial distortion, nationwide leverage, high Fed interest rates, and catalyzing news. Understanding the logic behind South Korea's circuit breakers offers valuable lessons for A-share investments and retail investors looking to avoid pitfalls.

I. First, reconstruct the full crash process: From frenzied rally to circuit-breaker collapse in just a few days
1. Extreme frenzy in the early stage, bubble fully inflated
Previously, the KOSPI had been on a relentless rally, surging from 8,000 points to a record high above 9,000 points in just over a month. Driven by AI memory chip demand, a nationwide stock-trading craze, and foreign capital inflows, a super bull market emerged. South Korean households moved savings into the stock market, with large numbers of ordinary people emptying deposits and borrowing money to buy stocks. The atmosphere of nationwide stock trading was at a fever pitch, completely detached from fundamentals, with pure liquidity pushing the index higher.
2. The trigger was just an "unofficial document with no seal"
The direct catalyst for the crash was merely a draft discussion on stock capital gains tax that had not been implemented. Rumors circulated that South Korea would tax unrealized stock gains and unrealized real estate profits, causing market panic that funds would flow out of the stock market in large volumes. The market opened lower and weakened from the start. Combined with a pullback in U.S. tech stocks, renewed expectations of Fed rate hikes, and collective weakness in Asia-Pacific stock markets, a confluence of multiple negative factors made the downward trend unstoppable.
3. Two circuit breakers triggered in succession, resulting in a deadly stampede
- Early morning: KOSPI200 futures fell over 5%, triggering the Sidecar mechanism, suspending all programmatic trading for five minutes, temporarily halting quantitative selling.
- Afternoon: The KOSPI index plunged past 8% and sustained for one minute, triggering a Level 1 full-market circuit breaker, suspending all stocks for 20 minutes. This was the fourth circuit breaker this year and the tenth in history (only six circuit breakers in the past 26 years, with four in a single year of 2026 being a spectacle).
- After the circuit breaker lifted, panic spread completely, with concentrated selling overwhelming the market. The index closed down 9.99%, a single-day plunge of 910 points, the largest single-day drop in nearly three decades. Key heavyweight Samsung Electronics fell 12.31%, SK Hynix plunged 12.47%, and the two memory giants directly dragged down the entire index.
4. Extreme divergence: Foreign capital flees frantically, retail investors trapped bottom-fishing with trillions
Foreign investors dumped over 2 trillion won (approximately $1.3 billion) in a single day, concentrated on selling core semiconductor heavyweights. In contrast, South Korean retail investors defiantly bottom-fished, with net purchases of 8.52 trillion won (approximately 37.6 billion yuan) in a single day, setting a historical record for daily retail buying in the Korean stock market. These bottom-fishing funds were deeply trapped on the same day, and they still face secondary liquidation from leveraged margin calls.

II. The four core underlying root causes of frequent circuit breakers in South Korea (the trigger is just the surface; the root causes were already embedded)
1. Extreme distortion in index structure: Semiconductors hijack the entire stock market with no buffer
The South Korean stock market is an extremely singular chip-dependent market: Samsung Electronics and SK Hynix, the two memory leaders, along with Samsung-affiliated companies, collectively account for over 50% of the KOSPI index weight. The entire market trend is completely tied to the AI memory chip cycle.
During the AI boom, the index soared; once global memory demand cools and chip price hike expectations retreat, either of the two giants can easily fall 10%+, causing the index to crash 8%+. With no sectors like consumer, healthcare, or financials to hedge, the index inherently has a "crash gene"—this is a congenital flaw that makes South Korea's stock market prone to circuit breakers.
2. Widespread high leverage among the populace is the most critical accelerator of circuit breakers (fatal hidden danger)
This is the most crucial culprit behind the crash: In late May, South Korea bulk-approved 16 2x leveraged ETFs tracking individual stocks, all linked to the two chip giants Samsung and SK Hynix. Retail investors could buy these 2x leveraged products with one click on their phones without needing margin accounts or risk control.
In just over a month, the size of these leveraged ETFs surged from $3 billion to $9.1 billion, with over 90% of holders being ordinary retail investors and a weekly turnover rate as high as 200%, effectively leveraging the entire nation on chip stocks.
Once stock prices fell slightly, the 2x leveraged products directly triggered a chain of forced liquidations: stock price drops → leveraged positions liquidated forcibly → further decline in stock prices → more leveraged accounts liquidated, forming an inescapable negative cycle. Within an hour, massive sell orders flooded in, smashing the index directly to the circuit breaker line. Even regulators later publicly regretted approving these leveraged products.
3. Foreign ownership is too high, making the market prone to collective exodus under high Fed rates
Foreign investors hold over 35% of the South Korean stock market overall, and more than half of semiconductor heavyweight stocks are foreign-owned, making it a market dominated by foreign capital pricing.
With the Fed maintaining high interest rates and renewed expectations of rate hikes this year, the U.S. dollar continues to strengthen, and global risk capital is flowing back to U.S. Treasuries. Once foreign investors collectively turn bearish and dump Korean stocks, there is no buying power to absorb the supply, causing the index to plummet rapidly. Compounded by the simultaneous depreciation of the Korean won, foreign investors are more inclined to sell and exit, further amplifying the decline. This is also an external driver of Korea's recent frequent circuit breakers.
4. Extreme emotional behavior of retail investors: Greed on rallies, panic on declines amplifies volatility
Retail investors account for over 60% of market turnover in South Korea, making them the dominant trading force: During uptrends, they blindly chase highs, pushing bubbles higher with nationwide leverage; during downtrends, they panic and stampede to cut losses, and negative rumors are magnified infinitely (an unenacted tax draft can smash the index by 10%). Moreover, retail bottom-fishing behavior is lagging; the more prices fall, the more they buy, only delaying the clearing process and lengthening the downtrend, turning circuit breakers from occasional events into a norm.

III. Four hardcore lessons for A-shares and ordinary investors from South Korea’s circuit breakers (most worth bookmarking)
Lesson 1: Absolutely stay away from high-leverage trading. Leverage is poison that makes small money in bull markets and loses principal in bear markets.
The outcome of South Korea's 2x leveraged ETFs has perfectly demonstrated this: Leverage only amplifies gains but also infinitely magnifies losses. In volatile and bear markets, leverage equals a liquidation accelerator.
A-shares have always strictly controlled margin trading and leveraged ETFs, limiting high multiples and tightening margin thresholds—essentially preemptively avoiding the kind of leveraged stampede circuit breakers seen in South Korea. Ordinary retail investors should never borrow money to trade stocks or touch products with 2x or higher leverage. This is the bottom line to avoid 80% of big losses.
Lesson 2: Do not put all eggs in one basket; balanced allocation is the key to withstanding declines.
South Korea suffered greatly from "betting it all on a single semiconductor track," with its index having no defensive sectors. In contrast, A-shares have multiple sectors such as finance, high-dividend stocks, consumer, healthcare, and cyclical industries to hedge. Even if semiconductors pull back, low-valuation sectors can support the index, making it very difficult to see a single-day drop of 8%+ triggering circuit breakers.
The same applies to personal investment: Do not go all-in on one industry or one stock. A balanced allocation of growth and value can help withstand extreme black swan events.
Lesson 3: Foreign capital flows are only short-term disturbances; domestic long-term capital is the market's ballast.
South Korea's biggest weakness is the small size of domestic long-term capital (pension funds, insurance). It does not provide support when markets rise and even sells off when they fall. In recent years, A-shares have been steadily expanding public funds, social security funds, insurance, and industrial long-term capital to reduce dependence on foreign capital. Even if northbound capital flows out short-term, domestic funds can absorb it, preventing extreme circuit-breaker scenarios.
Lesson 4: The kill power of negative rumors far exceeds that of implemented policies. In a news-driven market, always hold your hands.
The trigger for South Korea's big crash was just a discussion draft; the policy never actually materialized, yet the market preemptively dropped 10%. Capital markets always buy the rumor, sell the fact. The panic from vague negative news is far more damaging than the actual policy when implemented. In the future, when encountering various rumors and "small essays," don't panic and cut losses. First, verify the authenticity of the news to avoid being led by emotions into chasing highs and selling lows.