KOSPI Surges 3% and Triggers a Buy-Side Halt: Korea's Chip Rally Explained

South Korea's KOSPI closed up 3.09% at 5,638.35 on Tuesday, October 27, after rising so fast in the morning that the Korea Exchange triggered a buy-side sidecar — a five-minute suspension of program buy orders — when KOSPI 200 futures jumped more than 5%. Chip giants SK Hynix and Samsung Electronics led the surge, and Japan's Nikkei 225 rose 1.73% in the same AI-driven rally.

What happened on October 27?

The KOSPI opened strong at 5,658.65 and climbed as high as 5,737.61 before paring some gains into the close. At 10:13 a.m. Seoul time, KOSPI 200 futures were up 5.05% from the previous close and stayed there for a minute, which automatically triggered the buy-side sidecar, according to the Korea Exchange via the Seoul Economic Daily. Program buy orders were suspended for five minutes. It was the first buy-side sidecar since October 21, four trading sessions earlier — and the second such halt in six days.

By the close, the index had gained 168.87 points to finish at 5,638.35. The smaller KOSDAQ index also rose, ending up 2.29% at 743.83.

Which stocks led the rally?

Memory-chip makers carried the session. SK Hynix closed up 5.18% at 1,341,000 won, after rising more than 7% intraday. Samsung Electronics ended up 4.23% at 222,000 won. SK Square gained 7.67% and Samsung Electro-Mechanics rose 7.42%, while Samsung Biologics was a notable decliner, falling 5.37%.

Foreign and institutional investors drove the buying, with net purchases of 592.9 billion won and 282.0 billion won respectively, while retail investors sold a net 949.4 billion won, according to market data reported by Digital Today.

In Japan, the Nikkei 225 closed up 1.73% at 63,268.32. SoftBank Group surged 4.95% to 4,474 yen, while Kioxia edged up just 0.44%.

Why is it blowing up?

Three forces converged. First, Anthropic's filing for a U.S. initial public offering revived enthusiasm for the artificial intelligence trade after weeks of AI-bubble anxiety, Reuters reported. Second, U.S. chip stocks had jumped overnight — the Philadelphia Semiconductor Index rose 2.82%, its biggest one-day gain in a month, while the Nasdaq Composite added 0.82%. Third, bargain hunting: the KOSPI is still down about 17% in October despite Tuesday's jump, reflecting how steep the recent selloff in AI-linked shares had been.

Analysts cited by the Seoul Economic Daily said the Anthropic filing eased concerns about AI profitability, and expectations for AI chip demand revived as investors looked ahead to earnings from the very companies leading Tuesday's rally.

Key facts

• KOSPI close: 5,638.35, up 3.09% — intraday high 5,737.61.
• Buy-side sidecar triggered at 10:13 a.m. when KOSPI 200 futures rose 5.05%; program buying paused for five minutes.
• SK Hynix: +5.18% to 1,341,000 won. Samsung Electronics: +4.23% to 222,000 won.
• Nikkei 225: +1.73% to 63,268.32; SoftBank: +4.95%.
• Foreigners net bought 592.9 billion won; institutions net bought 282.0 billion won; retail net sold 949.4 billion won.

Sources: Reuters, Seoul Economic Daily, Longbridge / TradingKey, Digital Today, and BeInCrypto.

What's next?

The rally now faces an immediate test. SK Hynix reports earnings on Wednesday, October 28, and investors are watching its conference call for guidance on HBM4 chip yields and the timeline for a reported 16 trillion won special dividend. U.S. storage maker Seagate also reports, a cross-border signal for memory demand. Beyond that, more than a third of S&P 500 companies report this week, including Alphabet, Microsoft and Amazon, while the Federal Reserve, the European Central Bank and the Bank of Japan all hold policy meetings — economists expect all three to stand pat, leaving their commentary to move markets. Whether Tuesday was short covering or the start of a sustained rebound will likely be decided by those results, not by Tuesday's surge alone. This article reports what happened and why markets reacted; it is not financial advice.

FAQ

What is a buy-side sidecar?

It is a Korea Exchange safeguard that suspends program trading buy orders for five minutes when KOSPI 200 futures rise 5% or more from the previous close for at least one minute. It is designed to cool one-sided program buying, not to halt all trading.

How much did the KOSPI rise on October 27?

The KOSPI closed up 3.09% at 5,638.35, after briefly breaking above 5,700 intraday and triggering the buy-side sidecar in morning trade.

Why did Korean chip stocks surge?

Anthropic's IPO filing revived AI sentiment, U.S. chip stocks jumped 2.8% overnight, and buyers hunted bargains after the KOSPI's sharp October fall — all ahead of SK Hynix earnings on October 28.

Did other Asian markets rise too?

Yes. Japan's Nikkei 225 closed up 1.73% at 63,268.32, led by SoftBank's 4.95% gain, while South Korea's KOSDAQ rose 2.29%.