The Sword of Damocles Over the AI Bull Market: Not Just in South Korea, Leverage in U.S. Stocks Is Equally Staggering
Global equity markets are hitting new highs driven by the AI boom, but the fuel behind this rally is becoming increasingly dangerous. From the US to South Korea, margin debt and leveraged ETF assets have soared to historical extremes, with their pro-cyclical nature amplifying tail risks in market volatility.
In the US, margin debt rose 54% year-over-year in May, reaching a record $1.4 trillion. Simultaneously, leveraged ETF assets nearly doubled in under 70 days to over $220 billion by early June, with intense focus on tech, semiconductor indices, and single stocks like NVIDIA and Tesla. A warning sign appeared in South Korea, where the KOSPI index experienced extreme volatility, plunging 10% to trigger a circuit breaker, then sharply rebounding before halting again, partly driven by concentrated, highly leveraged positions in chip stocks.
Analysts are raising alarms. Barclays warns that leveraged funds have accumulated roughly $300 billion in equity-linked derivatives since late March, creating a major source of non-discretionary risk. Morgan Stanley notes an unprecedented reliance on leveraged financing by marginal buyers, with financing becoming more expensive and scarce. Charles Schwab has tightened margin requirements.
The core risk lies in the mechanics: leveraged ETFs and derivatives can create a "tail wags the dog" effect, where fund flows force market makers to buy underlying stocks, amplifying gains. This process reverses in a downturn, triggering a self-reinforcing selling spiral as funds deleverage. Additionally, the cost of borrowing to buy stocks has spiked to multi-year highs.
Morgan Stanley warns this sets up a nonlinear risk: high financing costs stall momentum, a price decline triggers forced deleveraging, and selling pressure is multiplied by leverage, potentially leading to outsized declines. The current market breadth is narrow, with gains heavily concentrated in tech, making the rally vulnerable to a pullback in leveraged positions.
In summary, the AI-fueled bull market is increasingly propped up by record leverage. When this trend reverses, the deleveraging process could magnify losses, posing a significant threat to financial stability.
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