Why did South Korean stocks just crash?

Noah Smith · Noahpinion · July 30, 2026 at 10:18 · ⏱ 11 min read  | Read on Substack ↗
Summary
Noah Smith argues that the recent crash in South Korean stocks was driven by a classic bubble-and-bust pattern: a strong fundamental AI story (memory chip demand) combined with financial leverage from retail investors using leveraged ETFs. The crash may foreshadow broader doubts about AI spending, as AI revenue growth ($150bn annualized) is far short of the ~$2.5trn needed to justify current capex, raising the risk of a larger tech sector correction.
  • •KOSPI surged from ~5,000 to over 9,000 in early 2026, then crashed back to ~5,500 within a month.
  • •SK Hynix operating profit jumped from under $10bn (Q1 2025) to over $35bn (Q1 2026) due to AI-driven memory demand.
  • •Korean retail investors borrowed heavily via leveraged single-stock ETFs to buy memory stocks, amplifying the boom and subsequent bust.
  • •AI revenue from major players (Anthropic ~$75bn annualized, others combined ~$150bn) would need to grow 17x to justify $2.5trn in AI capex.
  • •Chinese competitor Moonshot AI's model Kimi K3 nearly matches US models, threatening the moat of Anthropic and OpenAI.
  • •The 'Magnificent 7' index fell 11% from late May 2026, erasing $2 trillion in market value, as investors worry about AI spending ROI.
Read time 11 min
Length 11,478 chars
Category macro
Ideas
Noah Smith Economist; ex-columnist, Bloomberg Opinion
Article cites declining Nvidia stock chart and broader AI capex sustainability fears; notes that AI revenue must grow 17x to justify spending, risking a pullback in data center chip orders.
Article cites declining Nvidia stock chart and broader AI capex sustainability fears; notes that AI revenue must grow 17x to justify spending, risking a pullback in data center chip orders. Risk: If AI spending slows, Nvidia's revenue growth could decelerate sharply.
NVDA
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Micron (US top memory chip maker) shown with similar stock decline; memory demand is highly cyclical and tied to AI capex, which the article questions.
Micron (US top memory chip maker) shown with similar stock decline; memory demand is highly cyclical and tied to AI capex, which the article questions. Risk: Memory oversupply if AI demand disappoints.
MU
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GOOGL
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AMZN
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This newsletter, published July 30, 2026, features Noah Smith discussing NVDA, MU, MSFT, GOOGL, AMZN. 5 trade ideas extracted by AI with direction and confidence scoring.

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