South Korea’s KOSPI index surged more than 6% on the 20th, breaking through the 6,880 level, with a buy-side circuit breaker triggered during the session. Overnight measures by the U.S. Treasury Department to stabilize Treasury yields and a massive shareholder return policy announced by SK Hynix immediately after the previous day’s market close lifted investor sentiment.

According to the Korea Exchange, the KOSPI stood at 6,881.69 as of 10:52 a.m., up 410.52 points (6.34%) from the previous session. The index opened at 6,680.34, up 209.17 points (3.23%), before extending gains, with a buy-side circuit breaker triggered around 9:57 a.m. A buy-side circuit breaker is activated when KOSPI 200 futures prices rise more than 5% above the reference price for one consecutive minute, halting institutional investors’ program buy orders for five minutes.

With this, the KOSPI market has now seen 24 buy-side circuit breakers and 25 sell-side circuit breakers this year, totaling 49 circuit breaker activations. A sell-side circuit breaker was triggered just the previous day on the 19th.

The market shrugged off concerns about investment contraction stemming from the global rise in Treasury yields. In particular, SK Hynix, which announced a 40 trillion won (approximately $28.7 billion) share buyback and cancellation plan immediately after the previous day’s close, surged 12.73% to trade at 1.69 million won (approximately $1,200). Samsung Electronics rose 8.89% to 269,500 won (approximately $190), while Samsung Electronics preferred shares gained 9.33% to 189,900 won (approximately $140).

Buoyed by the sharp rally in large-cap semiconductor stocks, most top market-cap names advanced, including Hyundai Motor (1.81%), Samsung Electro-Mechanics (0.94%), LG Energy Solution (2.24%), Samsung Biologics (1.42%), and Samsung C&T (6.34%). SK Square also climbed 7.97%.

On the supply-demand front, foreign investors and institutions net bought 414.6 billion won (approximately $297.3 million) and 256 billion won (approximately $183.5 million), respectively, driving the rally. Retail investors, meanwhile, net sold 963 billion won (approximately $690.4 million). In program trading, arbitrage trades recorded net selling of 2.2 billion won (approximately $1.6 million), but non-arbitrage trades saw net buying of 251.5 billion won (approximately $180.3 million), resulting in an overall net buying position of 249.3 billion won (approximately $178.7 million).

The KOSDAQ index traded at 843.34, up 18.83 points (2.29%). Foreign investors net sold 119.8 billion won (approximately $85.9 million), while retail and institutional investors net bought 64.1 billion won (approximately $46.0 million) and 45.3 billion won (approximately $32.5 million), respectively. Alteogen, the largest KOSDAQ-listed company by market capitalization, surged 10.54% to 335,500 won (approximately $240), while EcoPro (3.71%), EcoPro BM (4.92%), Rainbow Robotics (3.35%), and Jusung Engineering (2.62%) all posted gains.

In Seoul’s foreign exchange market, the won-dollar exchange rate traded at 1,393.6 won, up 3.60 won from the previous session, still below the 1,400 won mark.

The sharp rally largely reflects bargain hunting following the previous day’s plunge. On the 19th, the KOSPI tumbled 5.8% to close at 6,471.17 amid Middle East geopolitical tensions and a spike in U.S. Treasury yields, with foreign investors net selling more than 3.5 trillion won (approximately $2.5 billion) in a single day. The 30-year U.S. Treasury yield surged to 5.33% intraday, its highest level since 2007, while Brent crude exceeded $91 per barrel.

However, overnight action by the U.S. Treasury Department to calm Treasury yields eased market anxiety, and SK Hynix’s massive shareholder return announcement provided a buy signal across the semiconductor sector. Securities analysts have noted that the previous day’s plunge was driven more by a pullback following short-term gains rather than any deterioration in corporate fundamentals.