Doosan Enerbility jumps 10.98%, SK Hynix 8.26% as the KOSPI adds 4.61% in a single session

1. Over 5 trillion won came in, leaving the index 4.61 points short of 7,000

The KOSPI closed at 6,995.39 on September 7, 2026, up 308.18 points, or 4.61%. That leaves the index 4.61 points below the 7,000 line.

The flow was one-sided. Foreign investors and institutions each bought more than 2 trillion won on a net basis, more than 5 trillion won between them, while retail investors sold over 6 trillion won. Days with a buyer this clearly identified are rare.

Rank the day’s gainers and power generation and construction sit at the top, with semiconductors behind them. That order is the character of the session: the stocks that built the index and the stocks that rose most were in different sectors.

2. Semiconductors did the lifting

SK Hynix rose 8.26% to 1,783,000 won. Samsung Electronics added 5.68% to close at 270,000 won. When the two largest companies in the market both gain more than 5%, the index moves on that alone.

Equipment and components followed. Jusung Engineering gained 4.99%, Hanmi Semiconductor 4.57% and Samsung Electro-Mechanics 3.78%.

The starting point was the previous U.S. session. After OpenAI put out a new model, buying concentrated in memory names, and Seoul took that flow straight from Monday’s open.

3. Nuclear power outran semiconductors

Doosan Enerbility closed at 87,900 won, up 10.98%. Among the stocks we follow, that was the largest advance of the session.

Nuclear-linked names did not move alone. Daewoo E&C gained 9.26%, carrying two stories at once: Middle East reconstruction work and overseas nuclear orders.

That power names outran chips on a day chips led the index is not a coincidence. A forecast of more AI data centres is a forecast of chip demand and electricity demand at the same time. The two sectors are the front and back of one story.

4. The previous session's winners were sold

ROBOTIS fell 0.99%, having surged 22.54% in the previous session. Rainbow Robotics fell 2.40%.

On the other side, Doosan Enerbility had been flat in the previous session and closed with a double-digit gain this time. In one session the money moved from robots to nuclear power.

That does not mean the robot story cooled. LG Electronics rose 6.20% the same day, and the reason was robots as well. What was bought and what was sold was decided by the specific catalyst, not by the sector label.

5. Not everything went up

By sector average, power generation and semiconductors led while consumer names and robotics lagged.

APR fell 2.54%, the steepest decline of the day, its fifth straight losing session.

Defence split internally. HD Hyundai Heavy Industries gained 2.86% while Hanwha Aerospace fell 1.52%. Biotech was quiet: Samsung Biologics rose 1.31%, while Celltrion and Alteogen both slipped less than 1%.

6. The KOSDAQ moved the other way

The KOSDAQ closed at 822.19, up 8.69 points or 1.07%, less than a quarter of the KOSPI’s advance.

The flow was the mirror image. On the KOSDAQ, retail investors bought a net 186.9 billion won while foreign investors and institutions both sold. Two markets in the same country, on the same day, with opposite hands at work.

The won closed at 1,343.1 per dollar, 0.47% stronger on the day, quoted at 16:38 by Hana Bank. On a regular-session close basis that is the strongest level in a year and eleven months, and the reasons cited most often in the currency market were yen strength and dollar selling by exporters.

Today's Foreign Investor Flows

What to watch next session

First, the 7,000 line. The index stopped 4.61 points short, so the answer comes within minutes of the next open. Holding it matters more than clearing it.

Second, retail supply. Whether the more than 6 trillion won sold this session keeps coming as the index rises, or stops here, is not yet knowable. The question is whether foreign and institutional buyers keep absorbing it at the same pace.

Third, U.S. rates. This was a chip-led advance, but the possibility of a rate increase has not gone away, and the further out a company’s profits sit, the more it reacts to that.

Fourth, the won. Around 1,340 is the strongest level in a year and eleven months. A stronger won makes continued foreign buying easier; a reversal will test how firm this session’s inflow really was.

Worth a closer look

Photo: Vishnu Mohanan / Unsplash

Explaining Seoul’s chip surge by saying U.S. stocks were strong is only half the story. In the previous U.S. session all three major indices fell: the Dow -0.51%, the S&P 500 -0.38% and the Nasdaq Composite -0.29%.

Memory went its own way on that same day. SanDisk gained 11.90% and Micron 6.10%, and the Philadelphia Semiconductor Index rose 3.38%. Apple fell 2.51% and Tesla 5.92%. A single market rarely splits this cleanly in one session.

Behind it sits GPT-6 Astra, which OpenAI put out on September 3. Sam Altman called the model a new capability level, and the market translated that into memory demand for training and inference.

So what Korea imported was not the U.S. market but one line of it. Given the weight Samsung Electronics and SK Hynix carry in the index, that one line is enough to move the KOSPI more than 4%.

Photo: Andrey Metelev / Unsplash

Doosan Enerbility’s 10.98% gain rests on two demand forecasts rather than a one-day headline.

The first is domestic. A revised power demand outlook prepared for Korea’s 12th Basic Plan for Long-Term Electricity Supply and Demand puts peak 2040 demand at 158.4GW, 26.6GW above the previous projection. The increase alone is equivalent to nineteen large 1.4GW reactors.

The second is American. A long-lead equipment procurement loan programme of up to 17.5 billion dollars, set up by the U.S. Department of Energy in June, reads as a signal that orders for reactors, steam generators and similar primary equipment will actually be placed. Doosan Enerbility builds exactly that.

Power demand forecasts do not change in a day the way share prices do. Material of this kind is better checked in the next quarter’s order announcements than in one session’s price move.

Stocks grouped under robotics went in different directions. Rainbow Robotics and ROBOTIS both fell, while LG Electronics rose 6.20%.

The reason is a subsidiary. Bear Robotics, the U.S. robotics company LG Electronics acquired, is pursuing a pre-IPO round of up to 400 billion won, with industry estimates putting its valuation in the high 2 trillion won range.

A component story was added on top. Baek Seung-tae, head of LG Electronics’ HS division, said the company is in order discussions with several global technology firms over robot actuators, with a meeting scheduled in October to check production readiness.

What the market bought was not finished robots but the parts that go into them and the stake in a company that makes them. That is consistent with two pure-play robot names falling the same day.

Among the stocks we follow, SK Square had the largest turnover of the session: 581.3 billion won traded, and the shares rose 8.07%.

The company does not make chips. What it holds is roughly 20% of SK Hynix, as its largest shareholder. When SK Hynix rises 8.26%, SK Square’s net asset value is recalculated in the same direction.

Holding company shares do not track their subsidiaries one for one. A discount is usually applied, and how far that discount narrows is the thing to watch on a day like this. SK Square gaining less than its subsidiary suggests the discount is still there.

A stock that moves on stake value retraces at the same ratio when the subsidiary does. That symmetry belongs in the calculation before a session like this one is read as a verdict.

Sources

• Asia Economy Korean-language article
• ifm.kr Korean-language article
• Money Today Korean-language article
• Money Today Korean-language article
• Etoday Korean-language article
• Edaily Korean-language article
• CBC News Korean-language article
• Korea Economic Daily Korean-language article
• job-post.co.kr Korean-language article
• SBS News KOSPI Reclaims 6,900 Mark on OpenAI Tailwinds, KOSDAQ Up 1%
• CNBC OpenAI announces rollout of GPT-6 Astra model