A single day saw a nearly 10% plunge, with circuit breakers triggered four times—an all-out, nationwide leveraged “stack” unwound into a catastrophic stock-market crash.

The most explosive event in the capital markets recently is none other than the normalization of circuit breakers in South Korea: the KOSPI plunged 9.99% in a single day to trigger circuit breakers across the entire market, with four circuit breakers occurring within the year to set a historical record; Samsung plus SK Hynix both crashed by more than 12%; trillions in leverage were liquidated in a chain reaction; foreign capital fled en masse; and retail investors’ trillion-yuan-scale bottom fishing ended with them trapped. This plunge is absolutely not a coincidence. It is a textbook stock-market disaster jointly triggered by industrial distortions, nationwide leverage, the U.S. Federal Reserve’s high interest rates, and news-driven catalysts. Understanding the logic behind South Korea’s circuit breaker mechanism offers strong reference value for A-share investing and for helping retail investors avoid pitfalls.

## I. First, reconstruct the full crash process: from a manic rally to a circuit-breaker collapse in just a few days

### 1. An extreme rally first, with the bubble inflated to the maximum
Earlier, the KOSPI surged relentlessly. In just over a month, it broke through 9,000 points to reach a new historical high, rising from 8,000 points. It rode a wave of AI storage-chip sentiment, a nationwide retail trading craze, and the inflow–outflow super-bull market driven by foreign capital. South Korean residents moved their savings into the stock market—many ordinary people emptied deposits and borrowed to buy shares—pushing the “everyone trading stocks” atmosphere to the limit. The market completely detached from fundamentals; pure liquidity alone pushed the index higher.

### 2. The fuse was only a “rumor document without an official stamp”
The direct cause of the crash was simply a draft discussing stock capital gains tax that had not been implemented: rumors circulated in South Korea that stocks with unrealized gains and real-estate gains that had not yet been realized would be taxed. The market panicked and anticipated that funds would massively flow out of the stock market—so in the early session it opened down and weakened immediately. Combined with a pullback in technology stocks in U.S. markets, renewed expectations of Fed rate hikes, and broad weakness in Asia-Pacific markets, multiple negative factors converged and the downward trend became completely unstoppable.

### 3. Two-tier circuit breakers triggered one after another, staging a deadly stampede
- **In the morning:** KOSPI200 futures fell by more than 5%, triggering the Sidecar mechanism. Programmatic trading was fully suspended for 5 minutes, and quant selling orders temporarily stalled.
- **In the afternoon:** The KOSPI index plunged by more than 8% and stayed that way for 1 minute, triggering a Level 1 full-market circuit breaker. Trading was paused for all stocks for 20 minutes. This was the fourth circuit breaker this year and the tenth in history (over the past 26 years there were only 6 circuit breakers; four in a single year in 2026 is truly remarkable).
- **After the circuit breaker ended:** Panic spread completely. Selling orders surged out in a concentrated wave. At the close, the market fell by 9.99%, losing 910 points in a single day and setting the largest single-day drop in nearly three decades. Samsung Electronics fell 12.31%, and SK Hynix fell 12.47%—the two memory giants directly dragged down the entire index.

### 4. Extreme divergence: foreign capital raced for the exits, and retail bottom fishers with trillions got trapped
In a single day, foreign capital dumped more than 20 trillion won (about 13 billion USD), concentrating on smashing semiconductor core heavyweight positions. In contrast, South Korean retail investors went against the trend and crazily chased the bottom: they net bought 8.52 trillion won (about 3.76 billion RMB) in a single day, setting a historical peak for daily retail stock purchases in the South Korean stock market. All of this bottom-fishing capital was deeply trapped on the same day, and afterward they would also face a second round of selloffs triggered by leveraged forced deleveraging.

## II. The 4 core underlying root causes behind South Korea’s frequent circuit breakers (the fuse is only a surface sign; the root causes were already buried)

### 1. The index structure is extremely distorted: semiconductors “bind” the entire stock market, with no cushion at all
The South Korean stock market is an extreme, highly single-chip-dependent market. Samsung Electronics and SK Hynix—the two memory leaders—together with Samsung-affiliated companies account for more than 50% of the KOSPI index weight. The overall market trend is fully tied to the AI storage-chip cycle.

When AI conditions are improving, the index surges wildly. Once global storage demand cools and expectations for chip price increases recede, the two giants can drop by 10%+ almost casually. Then the broader market directly collapses, falling by more than 8%. Without sectors such as consumer goods, healthcare, and finance to hedge, the index naturally has a built-in “crash gene”—this is the inherent hard flaw that makes South Korea’s market prone to circuit breakers.

### 2. Widespread leverage run amok is the most critical accelerator of circuit breakers (a fatal hidden risk)
This is the key culprit of this crash: by the end of May, South Korea approved a batch of 16 single-stock 2x leveraged ETFs, each tied to the two chip leaders—Samsung and SK Hynix. Retail investors do not need to open margin trading and securities lending accounts, and do not need to deal with margin-risk controls—just a single tap on a phone is enough to buy a 2x leveraged long product.

In just over a month, the size of this leveraged ETF batch surged from 3 billion USD to 9.1 billion USD. More than 90% of holders are ordinary retail investors, and the weekly turnover rate is as high as 200%—as if the entire population is using leverage to bet on the chip rally.

Once stock prices fall even slightly, 2x leveraged products directly trigger a chain of forced liquidation: stock price drops → leveraged positions blow up and are forced to sell passively → stock price drops further → more leveraged accounts blow up, forming an unsolvable negative feedback loop. Within a short hour, a massive wave of sell orders poured out, smashing the index down to the circuit-breaker line. Even regulators later publicly regretted approving these leveraged products.

### 3. Foreign ownership is too high, and with the Fed’s high interest rates, collective capital flight is easy
Overall, foreign investors hold more than 35% of South Korean stocks. For semiconductor leaders, foreign ownership is even more than half—meaning it is a market dominated by foreign investors’ pricing.

At present, the Fed maintains high interest rates and renewed expectations of additional rate hikes are returning. The U.S. dollar continues to strengthen, and global risk-asset funds flow back to U.S. Treasuries. If foreign investors collectively turn bearish and sell South Korean stocks in a concentrated way, there is no supporting capital to absorb the selling, and the index will quickly plunge in a cliff-like fall. Combined with the simultaneous depreciation of the South Korean won, foreign investors’ willingness to exchange currency and exit after selling increases further, magnifying the decline again. This is also an external push behind the frequent circuit breakers in recent years.

### 4. Retail sentiment is taken to extremes: blowout greed in rallies and panic in selloffs amplify volatility
Retail investors account for more than 60% of market trading volume in South Korea, making them the absolute trading force: in rising phases, they blindly chase and pile on positions, inflating the bubble; in falling phases, they panic and stampede to cut losses. Negative news rumors are amplified without limit—just an unimplemented tax draft could smash the 10% index. On top of that, retail bottom-fishing is lagging: the more prices fall, the more they buy, which only delays the clearing process, lengthens the downturn cycle, and turns circuit breakers from occasional events into a norm.

## III. Four hard-hitting lessons from South Korea’s circuit breakers for A-shares and ordinary investors (the ones most worth saving)

**Lesson 1: Keep far away from high-leverage trading—leverage is a poison that makes small gains in bull markets, and costs your principal in bear markets.**
The outcome of South Korea’s 2x leveraged ETFs has already provided a perfect demonstration: leverage only amplifies gains, and also infinitely amplifies losses. In volatile markets and bear markets, leverage is an accelerator of liquidation.

A-shares’ margin financing and trading (two-way lending) and leveraged ETFs have long been strictly controlled, with restrictions on higher leverage multiples and tightening of two-way lending thresholds. In essence, these measures preemptively avoid a leverage-driven, stampede-style circuit breaker like South Korea’s. Ordinary retail investors should never borrow money to trade stocks and should never touch 2x or higher leveraged products—this is the bottom line to avoid 80% of major losses.

**Lesson 2: A track cannot be taken to extreme single-mindedness—balanced allocation is the core to withstand declines.**
South Korea paid the biggest price for “betting the whole stack on a single semiconductor track,” and its index had no defensive sectors at all. By contrast, A-shares have multiple tracks for hedging, including financials, high-dividend sectors, consumption, healthcare, and cyclical industries. Even if semiconductors pull back, undervalued sectors can support the index, making it hard for a single-day 8%+ crash and circuit-breaker situation to occur.

The same applies to personal investing: don’t bet your entire position on one industry or one individual stock. You need balanced allocation of growth and value to stand up to extreme black-swan conditions.

**Lesson 3: Foreign capital flows are only short-term disturbances; local long-term capital is the market’s ballast.**
South Korea’s biggest weakness is that local long-term capital (pension funds, insurance) is too small. When markets rise, it does not step in to support; when markets fall, it sells in reverse. In recent years, A-shares have kept strengthening long-term capital such as public funds, social security, insurance, and industry funds—precisely to reduce reliance on foreign capital. Even if Northbound capital flows out in the short term, domestic funds can absorb the selling, so extreme circuit-breaker scenarios do not have to happen.

**Lesson 4: The killing power of negative rumors far exceeds that of implemented policies—if it’s a news-driven market, you must hold your ground.**
The fuse for South Korea’s selloff was only a discussion draft; the policy was never actually implemented, yet the market fell 10% in advance. In capital markets, you always buy expectations and sell facts. The panic generated by vague negative rumors has far more impact than policies once formally implemented. When you encounter all kinds of rumor “small essays” later on, do not panic and cut losses immediately. First verify whether the information is true or false, and avoid being driven by emotions into chasing rallies and then cutting losses.