South Korea's main stock market, the Kospi, posted its biggest one-day gain ever on July 31, 2026, rising about 15%. The jump was driven by a rebound in artificial intelligence stocks, with Samsung Electronics and SK Hynix each rising over 20% (KED Global; Moneycontrol). The rally followed a bounce in US stock markets the day before (Moneycontrol).

That surge came at the end of a brutal month. On July 28, the Kospi closed at 6,023.66, down 732 points, or about 11%, as a global selloff of chipmaker stocks deepened (Reuters). By then, the index had fallen 29% in July alone, its worst month on record. The drop continued on July 29, when the Kospi fell as much as 12.6% during the day, triggering a 20-minute trading halt (Reuters).

As of July 30, the Kospi had erased $2 trillion in market value from its June 2026 record high and dropped below the 6,000 level (Reuters). Yet just ten days earlier, on July 20, the index was still up 55% for the year after a strong prior year (Reuters). The swing from that position to below 6,000 took only about ten trading days.

The severity of the drop drew a response from regulators. South Korea's Financial Services Commission temporarily stopped new listings of certain high-risk investment products tied to single stocks and plans to raise the minimum deposit required to invest in them (Barron's). These products, called leveraged ETFs, aim to multiply the daily return of a single stock, so a 2x version tries to deliver twice the stock's daily move. The FSC had been discussing curbs on these products since at least July 8 over concerns that too much money was concentrated in them (Korea Herald). But the freeze and the deposit increase came after the selloff was already underway, not before it.

On the KOSDAQ, South Korea's smaller-company market, the Korea Exchange flagged NuriFlex for a closing-price swing covering July 30–31 and designated YesTech as an administrative-issue stock because its market value had fallen too low (KRX; KRX). Both actions are procedural risk warnings, not trading suspensions.

The broader context here is that the market's own structure made both the crash and the rebound worse. Those leveraged ETFs tied to stocks like Samsung and SK Hynix created a feedback loop. When the underlying shares fell, the leveraged products had to adjust their holdings to keep delivering the promised multiple, and that adjustment meant more selling into a market where buyers were already scarce. The FSC's halt on new listings stops more of these products from being created going forward. But the deposit increase, still in the planning stage, would not have stopped the automatic selling that happened during the July 28–29 plunge.

What the July 31 bounce does not fix is the situation of individual investors who held these leveraged products through the crash. A 15% gain in the index, even one that lifts Samsung and SK Hynix by over 20%, does not undo the losses on a leveraged position that went through a 29% monthly decline. Because these products multiply daily returns, a volatile stretch like July erodes their value faster than a simple percentage recovery can fix. The gain needed to break even is much larger than the loss that preceded it.

The question for anyone watching this market is whether the AI-sector rebound that drove the July 31 rally has real staying power or whether it is just investors who had bet against the market buying stocks back to close their positions after the July 30 US bounce. The facts establish what happened and why. They do not tell us whether the rebound will last or whether it is just a spike in a longer decline. The regulatory actions, the KOSDAQ warnings, and the $2 trillion in erased value all point to a market that moved beyond what its existing rules were built to handle.