Panic in Seoul: How a 12% Crash in Two Chip Stocks Triggered the AI Trade's Worst Day in Months

It started 7,000 miles from Wall Street, in a Seoul trading room, and within hours it had ripped through every major equity market in the world. On Tuesday, June 23, South Korea's benchmark Kospi index plunged nearly 10% — tripping the exchange's automatic circuit breaker not once but twice and forcing a 20-minute trading halt — as SK Hynix and Samsung Electronics, the two memory chip giants whose combined weight makes up roughly half of the entire index's market value, each crashed more than 12% in a single session. By the time the dust settled, the selloff had spread to Japan, Europe, and the United States, reviving a question that has been quietly building beneath this year's extraordinary AI-driven rally: is the artificial intelligence trade, in the words of one market strategist, simply "one big bubble"?

How the Crash Unfolded, Hour by Hour

The selloff that gripped global markets on Tuesday had its roots in a weaker session on Wall Street the day before. The Nasdaq fell 1.3% on Monday, dragged down primarily by a 5% drop in Alphabet shares amid concerns about high-profile AI talent departures at Google — an early tremor that, in retrospect, foreshadowed the much larger quake to come.

That tremor crossed the Pacific overnight and became something far more violent by the time Asian markets opened Tuesday. South Korea's Kospi, which had been one of the best-performing major equity benchmarks in the world this year — up roughly 95% year-to-date heading into the session — reversed with extraordinary speed. SK Hynix, the dominant global supplier of the high-bandwidth memory chips that power AI accelerators, and which had just one day earlier briefly overtaken Samsung Electronics to become South Korea's most valuable listed company, saw its shares crater more than 12%. Samsung Electronics, the world's largest memory chipmaker, fell by a similar margin. Because the two companies together account for approximately half of the Kospi's total market capitalization, their simultaneous double-digit collapse dragged the entire benchmark index down with them — at its worst point, the Kospi was off more than 10%, a decline severe enough to automatically trigger the Korea Exchange's circuit breaker mechanism, halting all trading for a cooling-off period not once but twice over the course of the day.

The contagion spread immediately and broadly. Japan's Nikkei 225 fell 3.5% to 3.6%, snapping a streak of eight consecutive positive sessions and giving back gains that had pushed the index to a record high just days earlier. Japanese technology conglomerate SoftBank, one of the world's most prominent AI infrastructure investors, sank 15% on the day. The small-cap Kosdaq index in South Korea fell nearly 8%. Hyundai Motor, an index heavyweight that had itself become a significant beneficiary of AI-linked investor enthusiasm, slid more than 12%.

Europe followed the same script when its markets opened. The continent's technology sector tumbled 3.1% as investors there joined the global retreat from AI-exposed names. Chip-equipment maker STMicroelectronics plunged 7.3%. Infineon Technologies slipped 5.4%, ASMI fell 5.9%, and Dutch lithography giant ASML dropped 4.9%. Germany's DAX shed nearly 1.3%, Italy's FTSE MIB slumped 1.36%, France's CAC 40 fell 0.79%, and the UK's FTSE 100 slipped 0.41%.

By the time US markets opened, Nasdaq 100 futures had already fallen as much as 2.6%, and S&P 500 futures were down roughly 1.4%, pointing toward a rough session even before the opening bell. When trading concluded Tuesday, the S&P 500 had fallen 1.44% to 7,365.46, and the tech-heavy Nasdaq Composite had slid 2.21% to close at 25,587.04 — marking its worst single day in roughly two weeks. The Dow Jones Industrial Average, far less exposed to the semiconductor sector, ended down just 45.87 points, or 0.09%, at 51,666.84, reflecting how concentrated the damage was specifically within AI-linked technology names rather than the broader market.

Which Stocks Took the Hardest Hits

The pain in the United States was concentrated almost entirely in semiconductor and memory chip names — precisely the corner of the market that had ridden the AI infrastructure buildout to its biggest gains over the preceding eighteen months. US-traded Micron Technology fell 13%, with much of that nervousness specifically tied to anticipation ahead of the company's quarterly earnings results, due the following day. Sandisk also dropped 13%. Storage components maker Seagate Technology shed more than 5%. Intel pulled back 6%, while Advanced Micro Devices and Qualcomm lost nearly 6% and 8% respectively. The State Street Technology Select Sector SPDR ETF (XLK) dropped 4%, and the VanEck Semiconductor ETF (SMH) — a fund that tracks the broader chip sector specifically — fell a full 7%.

Alphabet continued its multi-day slide, dropping a further 1% on Tuesday on top of Monday's 5% tumble, which had itself been driven by reports of senior AI talent departing the company. Not every technology name suffered, however — Microsoft and Amazon both rose even as chipmakers were routed, alongside a broader rotation into defensive consumer staples and healthcare names including Walmart, Procter & Gamble, and Johnson & Johnson. IBM shares popped 5% following an analyst upgrade to overweight at JPMorgan, while Sherwin-Williams and Merck also posted gains — evidence that the selloff was a targeted unwinding of a specific, crowded trade rather than a broad, indiscriminate market panic.

Why Now: The Forces Behind the Selloff

Several distinct but reinforcing factors combined to produce Tuesday's rout, according to market strategists and the broader financial press coverage of the event.

The most immediate and structural explanation is simply the scale of the run-up that preceded it. South Korea's Kospi had surged roughly 95% over the course of 2026 to that point, an extraordinary gain overwhelmingly powered by foreign investors pouring capital into memory-chip makers amid surging global demand for the advanced semiconductors used in AI servers and data centres. James Reilly, senior markets economist at Capital Economics, characterized the dynamic bluntly in a note to clients: "These big moves are part of a growing trend of rising volatility in tech stocks generally. This volatility is, in our view, evidence of excessive froth and calls into question the sustainability of this rally."

A second, distinct factor was last week's hawkish Federal Reserve meeting, which prompted traders to scale back their expectations for US interest rate cuts later this year — a development that disproportionately weighs on high-growth, high-valuation technology and AI stocks, whose worth depends heavily on future earnings discounted at prevailing interest rates. Higher-for-longer rate expectations make those distant future profits worth comparably less today, a mechanical valuation pressure that compounds whenever rate-cut hopes are pushed back.

A third and more existential factor concerns the underlying business case for the broader generative AI boom itself. NPR's coverage of the selloff noted that it arrived "at a moment when two of the largest AI companies, OpenAI and Anthropic, are considering selling their stocks to the market in what is shaping up to be two of the largest initial public offerings in history" — and that while both companies are now generating real revenue, "the long-term profitability of generative AI is an open question." Mark Vena, CEO of SmartTech Research, captured the market's underlying anxiety directly: "The market is trying to kind of digest all this and saying, 'Are we going to start to see returns?'" That question — whether the hundreds of billions of dollars being poured into AI infrastructure, chips, and data centres will ultimately generate commensurate profits — sits at the heart of the bubble debate that this week's crash has reignited.

A fourth, more geopolitically specific factor relates to the lingering aftereffects of the Iran conflict on regional economic data. Japanese purchasing managers index figures released this week showed that while both manufacturing and services activity picked up in June, input prices rose sharply due to disruptions caused by the broader Iran war and the Strait of Hormuz crisis that has dominated global energy markets for much of 2026. Iranian and US officials had reportedly made progress in fresh talks held in Switzerland over the weekend, helping ease some immediate concern over a sustained disruption to oil supplies — but investors remained cautious about the durability of any agreement, adding a layer of macro uncertainty to a market already nervous about AI valuations specifically.

A Bounce-Back That Raises Its Own Questions

By Wednesday morning, the panic had already begun to recede. South Korea's Kospi bounced back roughly 3%, and Samsung recovered much of its lost ground with a 7% surge — the latest in what CNN's coverage described as a recurring pattern of momentary dips that have punctuated the broader AI rally over recent months. Despite the severity of Tuesday's single-day plunge, the Nasdaq remained only about 5.5% below the record high it had set on June 2, and the tech-heavy index was still up roughly 10% for the year overall — context that several strategists pointed to as evidence the selloff, however dramatic in its mechanics, had not yet meaningfully dented the broader multi-month AI rally that has defined 2026's equity markets.

That quick partial recovery is itself part of the broader story analysts are now debating. A market structure capable of producing 10%-plus single-day declines in a major national benchmark, followed within 24 hours by a 7% single-day recovery in the very stock that drove the initial crash, is — almost by definition — a market trading on momentum, sentiment, and crowded positioning rather than on any rapidly shifting fundamental assessment of the underlying companies' actual earnings power. Whether Tuesday's rout was a healthy, overdue release of speculative excess in an overheated trade, or an early tremor preceding something larger, remains exactly the question that Wall Street, Seoul, and Tokyo are all now turning over as markets head into the back half of 2026.

Sources

1. CNBC — Stock market news for June 22, 2026
2. CNN Business — Wall Street is getting trampled by an AI sell-off. South Korean market plunges 10%
3. NPR — Is AI 'one big bubble'? Behind the tech sell-off
4. Investing.com — Asian stocks tumble as AI rout hammers KOSPI, triggers circuit breaker
5. Crypto Briefing — US chip stocks tumble after Asia's AI selloff raises bubble fears