South Korea’s KOSPI failed once again to hold above the 7,000 level despite a semiconductor rally sparked by OpenAI’s next-generation AI model launch. Heavy profit-taking by retail investors, seizing on the index’s upward momentum, overwhelmed simultaneous buying from foreign and institutional investors.

According to the Korea Exchange on September 9, the KOSPI closed at 6,954.52 the previous day, down 0.58% from the prior session. The index surged to 7,171.52 in early trading, crossing the 7,000 threshold for the first time since July 23, but gave back gains in the afternoon as retail selling intensified.

Institutions bought a net ₩932 billion (approximately $697.2 million) and foreign investors ₩658.2 billion (approximately $492.4 million), but retail investors dumped ₩3.3265 trillion (approximately $2.5 billion) worth of shares, pulling the index lower. Institutional and foreign buying continued for a fourth consecutive session but could not absorb the scale of retail selling.

The retail selling wall above 7,000 is formidable. According to Kiwoom Securities, retail investors’ net purchases at KOSPI levels of 7,000 or above total approximately ₩87 trillion (approximately $65.1 billion). Combined with financial investment accounts, the figure swells to ₩111.5 trillion (approximately $83.4 billion). By range, ₩18.9 trillion (approximately $14.1 billion) sits between 7,000–7,500, ₩30.2 trillion (approximately $22.6 billion) between 7,500–8,000, and ₩28.3 trillion (approximately $21.2 billion) between 8,000–8,500.

Han Ji-young, senior research fellow at Kiwoom Securities, said, “The retail positions above 7,000 are heavy. The reason the index repeatedly stalls at 7,000 is not fundamental deterioration but a combination of valuation multiples and retail selling pressure.” He added, “To digest the retail positions accumulated in this range, supply-demand momentum from foreign and institutional investors is needed.”

Semiconductor Rally Triggered by Astra

The backdrop to this latest push higher is OpenAI’s newest AI model, “GPT-6 Astra,” unveiled on September 4. Jensen Huang, CEO of Nvidia, wrote on social media: “Congratulations to OpenAI on ushering in the AGI (artificial general intelligence) era. GPT-6 Astra was trained on more than 100,000 Nvidia Grace Blackwell systems, and next, 400,000 GPUs will be brought online.”

Astra employs a “recurrence depth” architecture that performs computations iteratively. Because it repeats calculations until goals are achieved, total token consumption per task surges, strongly boosting demand for HBM bandwidth and ultra-high-speed networking. In practice, Astra completed Pokémon FireRed in 18 hours and 12 minutes, a clear performance leap over its predecessor.

Lee Kyung-min, an analyst at Daishin Securities, said, “OpenAI’s GPT-6 Astra has highlighted the possibility of reaching AGI with its high performance and utility. The prospect that AI token usage will grow as AI adoption spreads to diverse companies and developers has fueled AI infrastructure investment momentum, leading to strength in South Korean semiconductor stocks.”

The stock price reaction in semiconductor names was immediate. In the three trading sessions following the GPT-6 launch, Samsung Electronics rose 7.80% and SK Hynix gained 12.34%. On September 7 alone, Samsung Electronics surged 5.68% and SK Hynix jumped 8.26%, lifting the KOSPI by 4.61%.

The memory market outlook is also bright. KB Securities estimated that finished memory product inventories at Samsung Electronics and SK Hynix have plunged to under 10 days as of the third quarter. Goldman Sachs projected that supply-demand imbalances will deepen in 2027, with shortages persisting through 2028.

Foreign Optimism and Shifting Foreign Flows

Goldman Sachs is maintaining its KOSPI target of 12,000. Timothy Moe, Goldman Sachs’ chief Asia-Pacific equity strategist, said in an interview with Bloomberg: “We maintain our target because we believe the earnings we expect will be supported by semiconductor names. The market is not fully pricing in how long this earnings cycle will last.” Goldman Sachs forecasts a 360% net profit growth rate for KOSPI-listed companies this year.

Morgan Stanley last month set a KOSPI target of 9,000 and upgraded its rating from neutral to overweight. HSBC also raised its rating on South Korean equities from neutral to overweight. Nomura Securities issued a report maintaining its target prices of ₩670,000 (approximately $500) for Samsung Electronics and ₩4.7 million (approximately $3,500) for SK Hynix.

Foreign investor flows are also at an inflection point. From January through the end of August, foreign investors sold a net ₩170 trillion (approximately $127.2 billion) in the KOSPI, exiting the market. But in September, they flipped to net buying of over ₩1.4 trillion (approximately $1.0 billion). On September 7 alone, they bought a net ₩2.5137 trillion (approximately $1.9 billion), driving a KOSPI gain of nearly 5%.

However, short-term volatility factors remain. Net assets of three ETFs tracking the KRX Semiconductor Index have surged more than sevenfold in a year to ₩7.676 trillion (approximately $5.7 billion), with SK Hynix (36.9%) and Samsung Electronics (23.1%) both exceeding the 20% cap. Samsung Securities estimated that if the two stocks are rebalanced to 20% each during this month’s scheduled rebalancing, it would generate mechanical selling demand of ₩1.7 trillion (approximately $1.3 billion) combined. With the KOSPI’s average daily trading value having plunged from ₩50 trillion (approximately $37.4 billion) in June to ₩20 trillion (approximately $15.0 billion) this month, warnings are emerging that large one-way orders in a low-liquidity environment could amplify short-term volatility.

Absorbing the Retail Selling Wall Is Key

Market experts point to absorbing the retail selling wall as the key condition for the KOSPI to transition into a bull market. Retail investors, who sold ₩4.0505 trillion (approximately $3.0 billion) on September 4, sold a net ₩7.3432 trillion (approximately $5.5 billion) on September 7 and ₩3.3265 trillion (approximately $2.5 billion) on September 8 — dumping ₩14.7202 trillion (approximately $11.0 billion) over three sessions. During the same period, institutions bought a net ₩5.99 trillion (approximately $4.5 billion) and foreign investors ₩3.8163 trillion (approximately $2.9 billion). Retail investors sold more than institutions and foreign investors bought combined.

Na Jung-hwan, an analyst at NH Investment & Securities, said, “On June 1, combined trading value across KOSPI, KOSDAQ, and Nextrade exceeded ₩150 trillion (approximately $112.2 billion), but by September 2 it had shrunk to ₩35 trillion (approximately $26.2 billion). Depending on foreign investors’ direction in cash and futures markets, short-term stock price volatility could widen.”

The U.S. August Consumer Price Index (CPI), due this week, is another variable. The market expects headline CPI to rise 0.4% month-over-month and core CPI to rise 0.2%. As the final rate-related indicator before the September Federal Open Market Committee (FOMC) meeting, the result could sway foreign investor flows.

Yen strength has also emerged as a risk factor. With the yen entering the 152-per-dollar range for the first time in seven months (approximately $0.99 per 100 yen) and the Bank of Japan signaling a rate hike, concerns about yen carry trade unwinding are resurfacing. Investor caution is elevated given that carry trade liquidation fears triggered a sharp KOSPI selloff in late July.