The Korea Composite Stock Price Index, or KOSPI, closed at 6,995.39, its biggest one day gain since August 20 and 4.61 points short of the 7,000 level it has never reached.
The index added 308.18 points.
Foreign and institutional investors were net buyers together for a second consecutive session, after turning positive on Friday for the first time in six sessions. Their return ends a stretch in which corporate share buybacks were the main thing holding the Seoul market up.
Foreign investors bought a net 2.55 trillion won ($1.90 billion) on the main board. Institutions bought 2.63 trillion won ($1.96 billion). Individual investors sold 6.82 trillion won ($5.09 billion).
Samsung Electronics rose 5.7 percent to 270,000 won ($201.40).
SK hynix gained 8.3 percent to 1,783,000 won ($1,330.10), outpacing Samsung Electronics by more than two and a half percentage points. Foreign buying concentrated in the two large cap semiconductor names.
The buying followed a rally in U.S. memory stocks on Friday, when Micron Technology, SanDisk, Seagate Technology and Western Digital all advanced and the Philadelphia Semiconductor Index rose 3.4 percent.
The KOSDAQ, the secondary board for smaller and technology companies, rose 1.1 percent to 822.19. The KOSPI 200, which tracks the main board's largest listings, rose 5.1 percent, a wider gain than the main index itself.
The advance reached beyond memory. Doosan Fuel Cell rose 14.5 percent to 49,900 won ($37.20) and Doosan Enerbility gained 11.0 percent to 87,900 won ($65.60).
Doosan Fuel Cell disclosed last week a 501.4 billion won ($374 million) contract to supply phosphoric acid fuel cells to HyAxiom, the U.S. subsidiary of Doosan Corp., for an artificial intelligence data center. NH Investment and Securities raised its target price on the stock to 58,000 won from 34,000 won Monday and upgraded it to buy.
In Tokyo, memory maker Kioxia Holdings closed at 59,530 yen, up 9.3 percent, and SoftBank Group rose 11.2 percent to 6,217 yen.
Mitsubishi UFJ Financial Group fell 2.0 percent, leaving Japanese banks out of the advance even as traders position for a Bank of Japan rate increase this month.
Chinese chip and optical component makers followed the region higher. GigaDevice Semiconductor rose 3.2 percent to 383.88 yuan and Hengtong Optic Electric gained 3.2 percent.
PetroChina fell 1.3 percent, and the composite index in Shanghai closed roughly where it started.
The won closed at 1,340.5 to the dollar, 9.9 won stronger than Friday.
Monday was the fourth session in three weeks in which the main index in Seoul moved 4 percent or more. Even on this one, 381 stocks on the main board fell against 478 that rose. A repricing this concentrated in two names can be unwound as fast as it was built.
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