The benchmark KOSPI rose 0.73 percent to 6,345.53, extending gains for a second straight session. The index opened 0.95 percent lower at 6,240.06 before reversing course, though gains remained limited through much of the session.
The turnaround came after stronger export figures released shortly after the opening provided fresh momentum for chip stocks. The country's exports rose 45.3 percent from a year earlier to US$21.3 billion in the first 10 days of August, the highest level ever recorded for the period, according to preliminary customs data.
Semiconductor exports were a major driver, surging 155 percent to $10 billion. Chips also accounted for a much larger share of total exports, with their share rising about 20 percentage points from a year earlier.
The figures helped semiconductor heavyweights rebound from early weakness. Samsung Electronics climbed 4.13 percent to 239,500 won, while SK hynix edged up 0.35 percent to 1,425,000 won after falling around 3 percent earlier in the session.
The market's upside was limited, however, by continued uncertainty over the Strait of Hormuz. Reports overnight said Iran had rejected direct negotiations with the United States unless Washington ended sanctions and military threats and agreed to compensate Iran for war damage, leaving investors uncertain over prospects for reopening the key shipping route.
Trading flows were modest across investor groups. Foreign and institutional investors bought a net 44.3 billion won ($31 million) and 30.5 billion won worth of KOSPI shares, respectively, while individuals sold a net 70.7 billion won.
Foreign investors showed stronger buying in the futures market. They purchased a net 476.5 billion won in KOSPI200 futures, while institutions bought 123.3 billion won. Individuals sold a net 545.8 billion won.
Overall trading activity, meanwhile, increased from the previous session, with KOSPI turnover reaching 21.94 trillion won, about 2 trillion won higher than the prior day.
Market volatility also continued to ease. The KOSPI200 Volatility Index, or VKOSPI, fell 11 percent to around 61, its lowest level since early May. The decline followed a 7.99 percent drop Monday, when the index fell below 70 for the first time since late May.
Among other large-cap stocks, SK Square slipped 0.42 percent to 945,000 won, Samsung Electro-Mechanics lost 0.94 percent to 1,262,000 won, LG Energy Solution dropped 3.54 percent to 354,500 won and Hyundai Motor declined 1.23 percent to 403,000 won.
Samsung Biologics, meanwhile, rose 2.55 percent to 1,609,000 won, while Samsung Life Insurance gained 3.21 percent to 289,500 won and Samsung C&T advanced 2.53 percent to 344,500 won.
By sector, pharmaceuticals gained 3.02 percent, IT services rose 2.73 percent and insurance stocks added 2.47 percent. Transportation equipment and parts fell 3.37 percent, while metals lost 2.67 percent and food and tobacco declined 2.41 percent.
The junior KOSDAQ followed a similarly volatile path. The index closed 0.39 percent higher at 857.84 after swinging sharply between losses and gains.
It opened 0.69 percent lower at 848.59 and fell as much as 1.64 percent before surging as much as 2.42 percent. The index later gave up most of those gains before edging back into positive territory near the close.
Retail investors were the sole net buyers on the KOSDAQ, purchasing 435.1 billion won worth of shares. Foreign and institutional investors sold a net 360 billion won and 96.6 billion won, respectively.
Some of the KOSDAQ's largest stocks came under selling pressure. Alteogen, a biotechnology company and the KOSDAQ's largest stock by market capitalization, fell 5.89 percent to 327,500 won after a sharp gain in the previous session. Battery materials holding company EcoPro dropped 3.42 percent to 90,300 won, while its cathode materials unit EcoPro BM lost 4.36 percent to 109,800 won.
Semiconductor equipment and materials stocks bucked the weakness. Jusung Engineering surged 12 percent, Wonik IPS gained 6 percent and Jeju Semiconductor climbed more than 3 percent.
By sector, machinery and equipment gained 2.38 percent, distribution rose 2.12 percent and transportation and warehousing added 1.77 percent. General services fell 2.31 percent, while financials lost 1.45 percent and paper and wood declined 1.06 percent.
Trading turnover reached 6.77 trillion won on the KOSDAQ. Trading on alternative exchange Nextrade's pre-market and main-market sessions totaled 12.57 trillion won.
The Korean won strengthened to 1,417.50 per dollar from 1,418.40 at the previous close.
Regional markets showed a mixed picture, with Japan's stock market closed for the Mountain Day holiday in observance of Mountain Day, a national public holiday celebrated annually on Aug. 11 since 2016 to give people an opportunity to connect with nature and appreciate the blessings of mountains.
China's Shanghai Composite fell 0.82 percent to 3,934.09, while Hong Kong's Hang Seng Index was down 1.10 percent at 25,652.82 in late trading.
AJP Takeaways:
- South Korea's KOSPI rose 0.73 percent to 6,345.53 on August 11, 2026, reversing early losses and extending its winning streak to a second session.
- South Korean exports surged 45.3 percent year on year to $21.3 billion during August 1-10, 2026, the highest level ever recorded for the period, while semiconductor exports jumped 155 percent to $10 billion.
- Samsung Electronics gained 4.13 percent to 239,500 won and SK hynix rose 0.35 percent to 1,425,000 won, helping drive the KOSPI's intraday reversal.
- The KOSPI200 Volatility Index (VKOSPI) fell 11 percent to around 61 on Aug. 11, 2026, its lowest level since early May, signaling an easing in recent market volatility.
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