The main index in Seoul rose 240.20 points to 6,599.15 in the opening minutes.
The specific catalyst is SK hynix's own share count. The company issued 17.79 million new shares in a 45.45 trillion won third-party allotment to Citibank, N.A. to underpin its Nasdaq depositary receipts, and those shares listed in Seoul on July 29.
Traders read the enlarged base as an automatic increase in the stock's weight in MSCI benchmarks, forcing passive funds to buy.
SK hynix rose 5.9 percent to 1,670,000 won, or 1,169.71 dollars while Samsung Electronics gained 4.6 percent to 251,000 won, or 175.81 dollars.
Samsung Electro-Mechanics jumped 11.6 percent to 1,322,000 won, or 925.96 dollars, and SK square, which holds the group's stake in SK hynix, rose 7.8 percent to 1,143,000 won, or 800.59 dollars.
Foreign investors bought a net 299.2 billion won, or 209.6 million dollars, of KOSPI shares in early trade. Individuals sold 155.5 billion won and institutions 133.3 billion won.
The move extends a recovery from the July selloff that stripped Korean chip names of a large part of their first-half gain and pushed several domestic brokerages to cut second-half KOSPI targets.
The KOSDAQ, the secondary board for smaller and technology companies, lagged behind, rising 0.6 percent to 785.32.
The Nikkei 225 in Tokyo was up 2.3 percent at 65,443.37, a gain of 1,485.84 points, at the same hour.
The composite index in Shanghai closed Tuesday 12.62 points higher at 3,822.28.
The won was quoted at 1,427.70 to the dollar, stronger by 3.30 won.
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