The KOSPI closed at 7,096.89, up 299.19 points or 4.4 percent, while the tech-heavy KOSDOAQ rose 5.2 percent to 790.28, led by gains in biotechnology stocks.
Other major Asian markets moved in the same direction but with far less force, with Japan's Nikkei 225 rising 0.5 percent and China's Shanghai Composite barely changed.
SK hynix did the heavy lifting, closing at 1,919,000 won ($1,307.67), up 4.9 percent. Samsung Electronics rose 3.7 percent to 270,000 won ($183.99).
The gap between the two widened over the session. Traders read the split as positioning around high-bandwidth memory rather than a broad semiconductor rerating.
Samsung Electro-Mechanics outpaced both, gaining 7.7 percent to 1,448,000 won ($986.71). Institutions added a net 101.1 billion won ($68.9 million). Individuals sold 2.21 trillion won ($1.51 billion).
Market breadth was strong, with 831 stocks rising while 74 fell.
Energy equipment and electrical gear led the sector tables, with construction close behind, a rotation that puts the buying well beyond memory.
The KOSPI 200 added 4.3 percent to 1,126.33.
In Tokyo, Advantest rose 4.1 percent and SoftBank Group 3.8 percent, while Fast Retailing fell 1.9 percent.
The won traded at 1,467.50 per dollar, stronger by 11.50 won from the previous session.
The risk is that foreign buying of this scale may be driven more by index flows than by fundamentals, with such inflows into Seoul often proving short-lived.
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