South Korea's KOSPI Crashed 10% and Triggered a Second Circuit Breaker in a Week: Here's What Happened

South Korea's stock market experienced its most violent week in years in late June 2026. The benchmark KOSPI index plunged nearly 10% in a single session on June 23—an event dubbed "Black Tuesday"—triggering an automatic circuit breaker that halted all trading for 20 minutes. Just three days later, on June 26, the index crashed another 8.18%, forcing the Korea Exchange (KRX) to activate a second circuit breaker in the same week .

What caused this synchronized panic? Three major shocks hit simultaneously: Apple announced sweeping price increases on Macs and iPads due to a memory chip shortage, OpenAI surprised markets by signaling a delay to its blockbuster IPO, and a global rout in semiconductor and AI stocks erased billions in minutes.

The Two Circuit Breaker Events in Sequence

Black Tuesday (June 23)

The KOSPI plunged as much as 9.1–10% intraday on June 23, triggering a Level 1 circuit breaker at 2:33 p.m. KST. Some reports indicate breakers tripped twice during the session . The index closed at 7,484.41, down 8.29%, marking its steepest single-session decline since March 4 . The crash wiped out roughly 742.76 trillion won (about $485 billion) in market value in a single day . The panic was so intense that retail investors bought a record 8.54 trillion won into the collapse .

Friday's Second Circuit Breaker (June 26)

On June 26, the KOSPI crashed another 8.18%, triggering a circuit breaker at 12:10 p.m. KST . The Korea Times reported this was the fifth circuit breaker activation of the year . The sell-side was fueled by "heavy foreign and institutional selling over concerns of slowing memory demand amid broad chip-flation" .

What Caused the Sell-Off

1. Global Semiconductor and Memory Chip Correction

A broad-based rout in global semiconductor shares and growing fears that the memory chip earnings cycle had peaked spurred panic selling . The crash was described as a "direct window into the fragility sitting underneath the global AI trade" . The KOSPI had been up roughly 90% year-to-date before the rout, making it particularly vulnerable to a sharp reversal .

2. Apple Price Increases

On June 17, Apple CEO Tim Cook confirmed that "price increases are unavoidable" across Apple products due to an ongoing global RAM/memory supply shortage . Then, on June 25—just two days after Black Tuesday—Apple enacted those hikes. Mac computers jumped 15% to 20% in price, and iPads increased 15% to 25% . The MacBook Air, for example, rose from $1,099 to $1,299, and the MacBook Pro from $1,699 to $1,999 . Apple said it "could no longer shield customers from soaring memory and storage chip costs driven by the AI industry's datacenter buildout" . This amplified fears that elevated memory costs were hurting downstream consumer demand .

3. OpenAI IPO Delay

On June 25, the New York Times reported that OpenAI is leaning toward postponing its highly anticipated IPO until at least next year, and possibly to 2027 . Advisers presented options including waiting until 2027 for a $1 trillion valuation or lowering the target for a quicker listing . The delay signaled weakening near-term monetization expectations for the AI sector and hit sentiment hard. SoftBank Group shares tumbled 12% on the news, given SoftBank's large backing of AI ventures .

4. Fed Rate Hike Fears

Surging bets on a Federal Reserve double rate hike added to macro jitters . Global equities experienced a downturn driven by investors preparing for more stringent Fed actions to combat inflation, according to Reuters .

5. Leveraged Bets Compounding Losses

An increase in leveraged retail positions likely amplified the downside volatility, as Bloomberg noted that "intraday gyrations ran up the most in a month and an increase in leveraged bets likely compounded volatility" .

Hardest-Hit Companies

• Samsung Electronics and SK Hynix: These two memory-chip giants were ground zero of the semiconductor exodus. Both tumbled around 8–9% on June 8 and more than 10–12% on June 23 .
• Kioxia: The Japanese memory chip maker was among the hardest hit, along with other chip-equipment and AI-linked names across the region .
• SoftBank Group: Fell 12% on the OpenAI IPO delay news .
• Other large-cap names including Samsung SDI (-9%), LG Electronics (-12.7%), and Hyundai Motor (-10%) also suffered severe losses .

Asia-Pacific Market Performance (June 23)

Index	Change	Source
KOSPI (South Korea)	–10% (circuit breaker)
Nikkei 225 (Japan)	–3.55%
TAIEX (Taiwan)	–1.34%
Hang Seng (Hong Kong)	–1.82%
MSCI Asia Pacific Index	–3.6% (steepest since March)

India's Sensex and Nifty declined roughly 0.7–0.8% , and Shanghai finished in the red .

Broader Market Implications

U.S. Futures and Wall Street

Overnight signals from Wall Street indicated that tech and AI sectors "may have become over-extended after recent rallies," and U.S. tech stocks including Nvidia and Tesla experienced significant declines . The Nasdaq led the declines on Wall Street, burdened by semiconductor stocks as investors booked profits .

Expert Commentary — A Shift in Sentiment on Memory Chips and the AI Trade

Analysts at Investinq characterized the crash as a "direct window into the fragility sitting underneath the global AI trade" . The rout marked a sharp reversal after a record-breaking AI-fueled rally. One market summary described the trigger as "disappointing semiconductor forecasts" combined with "Middle East tensions and a Wall Street selloff" .

The combination of Apple's price hikes (transmitting memory-cost pain to consumers), OpenAI's IPO delay (casting doubt on AI monetization timelines), and Fed rate-hike fears caused a synchronized repricing of risk across the semiconductor supply chain.