South Korean shares closed marginally higher on Thursday as investors remained cautious after the U.S.-Iran war escalated.

Iran's Islamic Revolutionary Guard Corps (IRGC) launched retaliatory attacks at 18 US military targets at airbases in Kuwait, Bahrain, and Jordan, according to Iranian media reports. The strikes came after the United States military's Central Command (CENTCOM) said it had attacked multiple targets in Iran, describing the operations as acts of "self defense."

The Korea Composite Stock Price Index or Kospi rose 33.13 points, or 0.4%, to end at 7,763.95. The Kosdaq also increased by 45.3 points, or 4.5%, to close at 996.93.

In corporate news, Gaonchips (KOSDAQ:399720) secured an application-specific integrated circuit (ASIC) semiconductor design and development contract from an undisclosed AI semiconductor company, according to a Thursday filing with the Korea Exchange. The contract, valued at 29.6 billion won, is valid till June 30, 2028.

Shares of Gaonchips rose nearly 7% at market close.

In other news, SK Hynix (KRX:000660) plans to raise its wafer capacity by three times by 2034 to keep up with the increasing demand for memory chips needed for AI computing, SK Group Chairman Chey Tae-won told Nikkei Asia in an interview on Wednesday.

The chipmaker is currently building four semiconductor fabrication plants in South Korea's Yongin, with the first facility expected to be completed in early 2027. Chey said the company accelerated the project timeline by a decade, bringing forth a plan that was initially expected to run till 2045.

Shares of SK Hynix jumped nearly 3% at market close.