In the first half of 2026 the KOSPI nearly doubled in under a year, then closed out the period with a near-10% single-day crash. The index that had climbed roughly 100% year-to-date — the best return of any major market — pushed above 9,000 to an all-time high in the third week of June, only to be swept into record-setting volatility right afterward. The common thread running through the half is that both the driver of the rally and the trigger of the crash were “AI and semiconductors.”

Key takeaways (TL;DR)

  • The KOSPI surged about 100% in 2026, the top return among major global indexes, and set a record close of 9,114.55 on June 22.
  • The very next session, June 23, it plunged 9.99% and tripped a Level 1 circuit breaker; the roughly 910-point single-day drop was the largest on record.
  • The Bank of Korea’s base rate stands at 2.5% (held for an eighth straight meeting); the next Monetary Policy Committee meeting is July 16, with a hike on the table amid a hawkish tilt.

Why did the KOSPI lead the world in H1? Up about 100% year-to-date, the KOSPI rose more than any other major index in the first half of 2026. As early as the start of June, CNBC reported the “KOSPI is up 100% this year,” and Al Jazeera noted its value had “nearly doubled over the past six months,” effectively crowning it the world’s best-performing index. The engine behind the gains was large-cap memory-chip stocks riding expectations of expanding AI investment. But because the advance leaned heavily on a small number of large semiconductor names, it climbed fast on the way up while concentration risk and valuation strain grew in tandem.

What did the record on June 22 and the break above 9,000 mean? The KOSPI first closed above 9,000 on June 18 (9,063.84), then set a fresh record close of 9,114.55 on June 22. With the index — around 3,000 just over a year earlier — now past 9,000, the market read it as a blend of hopes for the “Korea discount” unwinding and gains from an “AI super-cycle.” Still, having doubled in such a short span, the market was structured so that even a small shock could unleash a wave of profit-taking — and that was confirmed almost immediately.

Why did it fall as much as -9.99% on June 23? On June 23 the KOSPI plunged 9.99% from the prior day, dropping in one move to around the 8,200 level. The roughly 910-point decline was the largest on record by points and ranked about fifth by percentage. As KOSPI 200 futures tumbled intraday, a sell-side sidecar was triggered, and in the afternoon — with the index down more than 8% — a Level 1 circuit breaker halted trading across the entire main board for 20 minutes. A sell sidecar had been triggered earlier on the KOSDAQ as well. The triggers are seen as a mix of: weaker-than-expected revenue guidance from some U.S. AI chip companies (Broadcom among them); concerns about profitability as Big Tech ramps up capital expenditure; and a stronger-than-expected U.S. jobs report that pushed back expectations for Fed rate cuts.

How did the volatility settle in the week after the crash? From the day after the plunge, the index swung sharply without finding direction. According to some tallies, the KOSPI rebounded about 3.3% on June 24 and about 5.4% on June 25, then fell roughly 5% again on June 26 to finish the week around the 8,400 level. The final session’s weakness is largely attributed to half-year rebalancing by global investors adjusting portfolios on an end-of-June settlement basis. Given the large intraday and daily swings, it is safest to confirm exact closing levels and percentage moves against official exchange (KRX) data.

What to watch in July: rates and the won The next inflection point for the market is monetary policy and the currency. The Bank of Korea’s base rate is currently 2.5%, held for an eighth consecutive meeting through May 28. That said, a dissenting vote favoring a hike emerged at the same meeting, and with the BOK signaling a hawkish stance over price and housing pressures, some now flag a possible hike as early as the second half. The next Monetary Policy Committee meeting is set for July 16. The won-dollar rate climbed into the high-1,530s won in late June as the won weakened; a persistently high exchange rate can weigh on foreign capital flows and import prices, so it is worth viewing alongside rates and equities.

The bottom line H1 2026 for the KOSPI can be summed up as a market that “AI lifted and AI shook.” A world-best return of roughly 100% year-to-date and record-setting volatility — a -9.99% circuit-breaker day — coexisted in the same quarter. The strong uptrend itself remains intact, but with the index leaning so heavily on a handful of large semiconductor stocks, the starting point for navigating the second half is to monitor three variables together: the AI chip cycle and Big Tech capex; the rate paths of the Fed and the Bank of Korea (the July 16 MPC); and the won-dollar rate alongside foreign flows. June made clear that the more sharply a market has surged in a short span, the more important managing volatility becomes.

※ This article is for informational purposes only and is not investment advice.

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