Korea Market Brief — KOSPI surges 4.61% to 6,995 as foreigners return to chip stocks (Sept 7)

Seoul spent the first week of September watching everyone head for the exit at once. On Monday, two of the three doors reversed direction — and the index moved 308 points.

The KOSPI closed at 6,995.39, up 4.61%, its single biggest one-day gain of a volatile fortnight and a whisker short of the 7,000 line. It never really wobbled: the index opened up 3.34% and extended from there. Foreign and institutional investors, both persistent net sellers through the previous week, turned buyers on the same day and pointed their money at the same place — memory chips.

The short version: Foreigners and institutions bought a combined 5.2 trillion won of Korean shares as an AI-driven memory-demand story reignited, lifting SK hynix 8.3% and Samsung Electronics 5.7%. The won firmed to a 23-month high against the dollar. Retail investors sold into all of it.

Korea Exchange close, Monday 7 September 2026 (KST).

What moved the market

The catalyst arrived from outside Korea. OpenAI's release of a new flagship model, GPT-6 Astra, landed late last week to strong reviews, and the read-across in Seoul was immediate and mechanical: more capable models mean more tokens processed, more inference infrastructure, and more high-capacity memory to feed it. Nvidia's separate announcement that it will acquire Hugging Face reinforced the same thesis. Wall Street had already priced part of it — the three main US indexes fell on Friday 4 September, but the Philadelphia Semiconductor Index rose 3.38%, and that divergence is what Seoul picked up on Monday morning.

What made the reaction so violent is where Korean chip stocks were starting from. Samsung Electronics and SK hynix had fallen roughly 38% from their three-month peaks, dragging their valuations down to around three times projected 2027 earnings. Any credible demand signal into a setup like that produces an outsized move.

The flows tell the story cleanly. Foreign investors net bought 2.59 trillion won (about $1.93 billion) and institutions net bought 2.63 trillion won. Retail investors net sold 6.82 trillion won — an enormous number, and a reminder that domestic individuals have been distributing into every bounce for weeks.

That reversal matters more than the headline percentage. Through 4 September, the unusual condition in Seoul had been that retail, foreign and institutional investors were all net sellers at the same time, with corporate share buybacks — Samsung's and SK hynix's own repurchases, which the exchange counts under "other corporations" — absorbing the supply. Buybacks can stop an index falling. They cannot push it up 4.6%. For that you need foreigners, and on Monday foreigners showed up.

Sector by sector

Semiconductors did essentially all the work, and the strength broadened as the session went on. Beyond the two large caps, the rally reached back-end processing, packaging, materials and equipment names — the second tier that typically lags the leaders on the way up. Doosan Tesna traded up more than 12% intraday, DB HiTek gained double digits, and PSK Holdings, Tes, Eugene Technology, Soulbrain and Wonik IPS were all firmer. Sell-side desks have been arguing for a rotation back into IT materials and equipment on valuation grounds; Monday was the first session in a while where the market agreed.

The 1.07% gain on the KOSDAQ against 4.61% on the KOSPI is the clearest read on how narrow this was. This was a large-cap, export-facing, memory-specific rally, not a broad risk-on day. Sectors with no AI supply-chain exposure participated only modestly.

The supply argument underneath it is the part worth understanding. KB Securities estimates that memory inventories at the two Korean chipmakers fell below 10 days in the third quarter, and notes that HBM4 consumes roughly three times the wafer capacity of commodity DRAM — meaning every unit of high-bandwidth memory built crowds out substantially more conventional supply. On that arithmetic, the brokerage sees 2027 DRAM and NAND demand potentially exceeding supply by more than 10 percentage points. Nomura made a related structural point: global memory capacity would need to roughly double within four years and triple within six to meet projected demand. Several brokerages raised their estimates on the two chipmakers on Monday. Whether those forecasts prove right is a different question — but they explain why the bid was so aggressive.

The won and the macro picture

The won closed at 1,340.5 per dollar, stronger by 9.9 won, after touching 1,338.5 shortly after the open — its firmest level in 23 months. Equity inflows explain part of it: 2.59 trillion won of foreign buying has to be funded in won.

The rest is a dollar story with a Japanese accent. The yen has appreciated from around 160 per dollar to the 155 range, which is reviving talk of a yen carry-trade unwind — a dynamic that tends to pull capital back toward Asian currencies broadly and has caught markets off guard before. Traders are watching it closely.

Working against that is the US rate picture. August payrolls came in at 162,000 against a consensus near 55,000, with unemployment steady at 4.1%. That was strong enough to revive talk of a Federal Reserve hike this year rather than a cut, and it pushed the 2-year Treasury yield to its highest since January 2025. A market that has repriced from cuts to possible hikes is not a comfortable backdrop for a heavily foreign-owned emerging market — which is one reason Korean equities have been so erratic, swinging from a 3.99% drop on 2 September to Monday's 4.61% gain inside four sessions.

The valuation gap is the other half of the setup. Bloomberg-compiled 12-month forward price-to-earnings ratios put the US and Taiwan near 20 times, Japan around 16 and China around 11 — with Korea below five. Cheap markets stay cheap until a catalyst arrives; Monday supplied one. Note that US markets were closed on Monday for Labor Day, so Seoul traded without a live New York session to check itself against, which likely amplified the move.

What to watch next

• Tuesday 8 September: The Bank of Korea publishes its revised Q2 GDP figure. The advance estimate showed 0.6% quarter-on-quarter growth, well above the central bank's own 0.2% projection, with semiconductor exports doing much of the lifting. Nominal Q2 GDP lands the same day, and the governor has signalled it should be notably strong.
• Thursday 10 September: The European Central Bank's rate decision.
• Friday 11 September: US August CPI, currently forecast around 3.4% year-on-year. Given how Friday's payrolls print moved yields, this is the week's largest single risk to Seoul.
• Ongoing: DRAM and NAND spot pricing, HBM4 qualification news, and whether foreign investors keep buying. A single day of inflows is not a trend.

Monday answered the question of whether Korean chip stocks were cheap enough to attract a bid. It did not answer whether foreign money is back for good, and with US inflation data landing Friday, that question stays open for at least another week. The 7,000 level sits directly overhead.

This is market information, not investment advice.