KOSPI surges 6.2% as Samsung, SK hynix lead chip rally in Seoul
Synopsis
SK hynix's announcement of a ₩40 trillion share buyback — one of the largest in South Korean corporate history — sent its stock soaring 12.27% and dragged the entire KOSPI up 6.2%, triggering a regulatory circuit breaker. Combined with retreating US Treasury yields, Seoul's chip sector staged one of its sharpest single-session recoveries in recent memory.
Key Takeaways
KOSPI rose 401.44 points , or 6.2 percent , to 6,872.61 as of 11:20 am on 20 August .
SK hynix surged 12.27 percent after announcing a ₩40 trillion (US$28.7 billion) share buyback plan.
Samsung Electronics jumped 8.99 percent ; SK Square gained 9.21 percent .
Korea Exchange (KRX) activated a buy-side sidecar, suspending programme trading for five minutes at around 10 am .
The rally was supported by retreating US Treasury yields after the Treasury Department announced plans to buy back longer-term government debt.
The Korean won softened to 1,394.4 per US dollar, down 5.3 won from the previous close.
Seoul's benchmark Korea Composite Stock Price Index (KOSPI) surged 6.2 percent on Thursday, 20 August, as investors aggressively bought into major chipmakers, with Samsung Electronics and SK hynix leading the charge on expectations of stronger shareholder returns. The index climbed 401.44 points to 6,872.61 as of 11:20 am local time, after opening 3.23 percent higher.
Circuit Breaker Triggered at Open
The scale of the morning rally was sharp enough to activate a regulatory safeguard. Korea Exchange (KRX) suspended programme trading for KOSPI-listed shares for five minutes at around 10 am, triggering a buy-side sidecar — a measure activated when the KOSPI 200 Futures Index rises 5 percent or more for at least one continuous minute. The activation underscored the velocity of buying pressure in the session.
Chip Giants Drive the Rally
Chipmakers rebounded sharply from losses in the prior session. Samsung Electronics jumped 8.99 percent, while its rival SK hynix surged 12.27 percent — a day after the company announced plans to buy back 40 trillion won (approximately US$28.7 billion) worth of shares to enhance shareholder returns. The buyback announcement was a key catalyst for the broader semiconductor-led rally.
SK Square, the parent company of SK hynix, advanced 9.21 percent. Samsung Electro-Mechanics, an electronics component affiliate of Samsung Electronics, posted a more modest gain of 0.65 percent.
Wall Street Tailwind and Treasury Yields
Overnight momentum from Wall Street added fuel to the Seoul rally. Major US indexes closed higher after the US Treasury Department announced plans to significantly increase buybacks of longer-term government debt, which pulled yields lower. The 30-year Treasury bond yield — which had climbed to its highest level since 2007 — retreated on Wednesday, as did the benchmark 10-year Treasury yield. Lower US yields typically reduce the appeal of bonds relative to equities, supporting risk appetite globally.
Currency and Broader Market
The Korean won traded at 1,394.4 won against the US dollar as of 11:20 am, down 5.3 won from the previous session's close — a modest depreciation that analysts note can marginally boost export-oriented chipmakers' earnings when converted back to won. This comes amid a broader regional equity recovery, with semiconductor stocks across Asia finding support from both the US yield retreat and company-specific buyback signals.
Point of View
A shift that mirrors what US tech giants did a decade ago when growth plateaus forced a rethink of cash deployment. The KOSPI's 6.2% single-session surge also exposes how heavily the index is tethered to semiconductor sentiment; when chips sneeze, Seoul catches a cold — and vice versa. The buy-side sidecar activation is a reminder that Korean retail investor participation remains intense, amplifying both upswings and downturns. Whether this rally sustains will depend less on Seoul and more on whether US yield pressure abates and global AI-driven chip demand holds through the next earnings cycle.
NationPress
20 Aug 2026
Frequently Asked Questions
Why did the KOSPI surge more than 6 percent on 20 August?
The KOSPI rose 6.2 percent to 6,872.61 on 20 August, driven by a sharp rally in chipmakers Samsung Electronics and SK hynix. The gains were fuelled by SK hynix's announcement of a ₩40 trillion share buyback and a positive Wall Street session overnight as US Treasury yields retreated.
What is the SK hynix share buyback plan?
SK hynix announced plans to buy back ₩40 trillion worth of its own shares — equivalent to approximately US$28.7 billion — to boost shareholder returns. The announcement was made a day before Thursday's rally and was the primary catalyst for the stock's 12.27 percent surge.
What is a buy-side sidecar and why was it triggered?
A buy-side sidecar is a circuit-breaker measure used by the Korea Exchange that temporarily suspends programme trading when the KOSPI 200 Futures Index rises 5 percent or more for at least one minute. It was triggered at around 10 am on Thursday due to the speed and scale of the morning's buying surge.
How did Wall Street influence the Seoul rally?
US markets closed higher overnight after the Treasury Department announced plans to increase buybacks of longer-term government debt, which pushed the 30-year Treasury yield — near its highest since 2007 — sharply lower. Retreating yields improved global risk appetite, supporting equities in Seoul and across Asia.
How did the Korean won perform during the rally?
The Korean won weakened slightly, trading at 1,394.4 won per US dollar as of 11:20 am on Thursday, down 5.3 won from the previous session's close. A softer won can provide a marginal earnings boost for export-oriented chipmakers when overseas revenues are repatriated.
