The Seoul benchmark opened higher after plunging 17 percent over the previous two sessions, but selling in heavyweight chip stocks quickly erased the gains. As of 9:50 a.m., the KOSPI was down 0.74 percent at 5,621.47.
Samsung Electronics rose 1.0 percent on record second-quarter operating profit of 89.49 trillion won ($62.2 billion) while SK hynix fell 5.1 percent, with shipbuilders, defense contractors, refiners and banks carrying the recovery.
Gainers overwhelmed decliners 673 to 210 with foreigners buying net 214.5 billion won and local institutions 300.6 billion won.
Samsung Electronics traded at 210,500 won ($146) after reporting an all-time high in quarterly operating profit, up 1,813.8 percent from a year earlier.
Revenue reached 171.5 trillion won and net profit 71.62 trillion won. Operating profit landed above analyst estimates while revenue fell slightly short.
Almost all of the profit came from one place. The Device Solutions division, which houses the semiconductor business, accounted for 89.2 trillion won of the total.
SK hynix dropped to 1,329,000 won ($923), a day after reporting record operating profit of 60.5 trillion won ($42.0 billion) on revenue that came in below what the market wanted.
Its New York listing offers a second read on the same company. SK hynix ADRs closed at $126.79 on Wednesday, down 2.6 percent, with each receipt representing one-tenth of a Seoul share and two-way conversion between the two lines now open.
SK square, which holds the group's stake in SK hynix, fell 5.8 percent to 801,000 won ($557), a steeper drop than the chipmaker itself.
The KOSPI 200 was little changed, up 0.1 percent against the broader index's 0.4 percent advance, a gap that shows the largest names still lagging the rebound.
Individual investors sold a net 518.3 billion won of KOSPI shares in the opening minutes, selling into the recovery rather than buying it. Foreign investors bought a net 190.3 billion won and institutions 314.5 billion won.
Retail buyers had already broken pattern. They net sold 1.406 trillion won on Wednesday rather than buying the drop, ending a run of heavy dip-buying that had cushioned earlier selloffs this year.
Crude prices climbed overnight on escalating Middle East tensions, and Seoul's cyclicals moved with them. Shipbuilding led sector gains at 6.7 percent, with aerospace and defense up an identical 6.7 percent and refining shares close behind.
Hanwha Aerospace jumped 8.5 percent to 879,000 won ($611) and HD Hyundai Heavy Industries gained 4.5 percent to 453,500 won ($315). Banks also drew buyers, with KB Financial up 5.5 percent at 168,900 won ($117).
The KOSDAQ, which triggered its own halt on Wednesday, rose 1.2 percent to 670.74, outpacing the main board.
In Tokyo, the Nikkei 225 traded at 62,014.53, up 0.9 percent.
The won was quoted at 1,439.20 to the dollar, 6.80 won firmer than the previous session.
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