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South Korea KOSPI falls 2.08% for week: AI chip doubts (Oct 23)

Seoul's main index moved more than 3% in three of five sessions as AI spending worries and foreign selling hit chipmakers, while the Bank of Korea held rates at 3.00%. SK hynix's Solidigm decision helped Friday's late rebound.

By Rowan Ashby Published 23.10.26 09:36 UTC 7 min read

KOSPI Composite Index price chart over the past 5 days, -0.08% — Illustration: Bullquill chart, data: Yahoo Finance (original)

Key takeaways

The KOSPI fell 117.75 points, or 2.08%, in the week to Friday, October 23, 2026, closing at 5,550.30, against 5,668.05 a week earlier.
The KOSDAQ dropped 5.42% to 751.69, a steeper fall than the main board's.
The KOSPI moved by more than 3% in three of the five sessions. Each time, investors were reacting to news about AI spending and chip demand.
The Bank of Korea kept its base rate at 3.00% on October 22. All seven Monetary Policy Board members voted for the hold.
Foreign investors sold a net 1.0938 trillion won of KOSPI shares on Friday, according to Seoul Economic Daily. Late buying in SK hynix, which rose 4.42% after it halted a US IPO review for Solidigm, lifted the index into positive territory.

Week in review

The KOSPI ended a whipsaw week lower. The previous week, on October 15, it had fallen 7.57% and triggered a circuit breaker. This week, news on US AI spending drove the market: strong AI server data lifted chipmakers on Wednesday, then Meta's weak cash flow pulled them down. See all market briefs.

South Korean markets, week to October 23, 2026
Instrument	Prior week close (Fri)	Week close (Fri)	Weekly change	% change	Week high / low	As of (UTC)	Source
KOSPI	5,668.05	5,550.30	−117.75	−2.08%	5,816.43 / 5,305.98	2026-10-23 06:30	Investing.com (KRX data); Seoul Economic Daily
KOSDAQ	794.78	751.69	−43.09	−5.42%	808.92 / 732.87	2026-10-23 06:30	Investing.com (KRX data); Seoul Economic Daily
USD/KRW (won per dollar)	1,334.61	1,325.11	−9.50	−0.71%	1,338.24 / 1,320.09	2026-10-23 09:30	Investing.com
Samsung Electronics (won)	215,500	215,500	0	0.00%	228,000 / 203,500	2026-10-23 06:30	Investing.com; Korea JoongAng Daily
SK hynix (won)	1,272,000	1,277,000	+5,000	+0.39%	1,329,000 / 1,172,000	2026-10-23 06:30	Investing.com; Seoul Economic Daily

KRX closes at 15:30 KST (06:30 UTC). The USD/KRW figure is Investing.com's global quote at 09:30 UTC on October 23. A lower USD/KRW means a stronger won.

Daily closes, October 19–23, 2026
Day	KOSPI close	Change	Change %	KOSDAQ close	Change %	As of (UTC)
Mon, Oct 19	5,768.01	+99.96	+1.76%	808.89	+1.78%	2026-10-19 06:30
Tue, Oct 20	5,552.74	−215.27	−3.73%	781.97	−3.33%	2026-10-20 06:30
Wed, Oct 21	5,735.66	+182.92	+3.29%	792.76	+1.38%	2026-10-21 06:30
Thu, Oct 22	5,533.77	−201.89	−3.52%	764.10	−3.62%	2026-10-22 06:30
Fri, Oct 23	5,550.30	+16.53	+0.30%	751.69	−1.62%	2026-10-23 06:30

Source: Investing.com historical data, cross-checked against Seoul Economic Daily, MoneyToday and UPI closing reports.

Day by day

Monday: The KOSPI recovered from early losses to gain 1.76%. Institutions bought battery and biotech shares after the previous week's slump, KED Global reported. President Lee Jae Myung said a correction was inevitable after the rally and that Korean stocks remain undervalued, according to Bloomberg.
Tuesday: The index fell 3.73%. Foreign investors sold a net 542 billion won and institutions 998 billion won, while retail investors bought 901 billion won, according to UPI. Samsung lost 2.98% and SK hynix 4.23%.
Wednesday: The KOSPI rose 3.29%. Samsung gained 5.67% to 223,500 won and SK hynix 5.81% to 1,294,000 won. Seoul Economic Daily linked the rally to Super Micro Computer's preliminary revenue and a 222.5% jump in chip exports, to $27.52 billion, in the first 20 days of October. It said a buy-side sidecar was triggered for the first time since August 20.
Thursday: The index lost 3.52%, with Samsung down 4.03% and SK hynix down 5.49%. MoneyToday reported net selling of 683.3 billion won by institutions and 399.1 billion won by foreigners. The Asia Business Daily's foreign figures differ, so treat them as provisional.
Friday: The KOSPI opened 2.36% lower and touched 5,305.98, then closed up 0.30%. Foreigners sold a net 1.0938 trillion won, while institutions bought 795.5 billion won and retail investors 233.6 billion won, according to Seoul Economic Daily.

What drove it

AI spending and the memory-chip trade

Samsung Electronics and SK hynix make up a large share of the KOSPI, so the index tracks US news on AI spending closely. On Wednesday, Super Micro's revenue estimate of $18.5 billion to $19.5 billion beat the $14.95 billion consensus, according to Seoul Economic Daily. On Thursday in New York, the Nasdaq fell 2.6% and Micron 6.26%, Korea JoongAng Daily reported. MoneyToday tied the drop to concern that Meta's cash flow had turned negative as it funds AI investment. For the US side, see why the Nasdaq fell on AI spending worries and the slump in US chip stocks.

Company news: SK hynix and Solidigm

Before Friday's open, SK hynix said in a regulatory filing that it had halted its review of a US IPO for Solidigm, its NAND and SSD unit. Investors had feared dilution from a second listing, Seoul Economic Daily reported. Meritz Securities analyst Kim Sun-woo told the paper that the decision could lead to stronger shareholder returns at the third-quarter earnings call on October 28. Daishin Securities researcher Lee Kyung-min told MoneyToday that the end of an SK hynix share buyback on October 21 had left the market less able to absorb selling.

Foreign flows and the won

Foreigners sold on Tuesday and Friday, and on Thursday by MoneyToday's count, but bought on Wednesday. Retail investors absorbed much of the selling. The won firmed slightly over the week. The Bank of Korea credited the won's recent strength partly to a large current account surplus.

Oil and the Middle East

Brent crude rose 4% to $113.17 a barrel on renewed US-Iran tensions, MoneyToday reported. The BoK said that escalation in the Middle East had pushed up oil prices and Korean bond yields.

Political & policy watch

Bank of Korea. The board held at 3.00% after hikes in July and August. The BoK said September consumer prices rose 2.9% (core 2.8%) and that growth in 2026 and 2027 should be considerably higher than its August forecasts of 3.3% and 2.9%. It "sees it warranted to continue its policy response" until it is confident that inflation will settle at target. The timing of any further hike will depend on data, including third-quarter GDP and October inflation.

Presidential office. Bloomberg reported that President Lee planned to take necessary measures after a briefing. None had been published by Friday's close.

Regulators. Financial regulators had said an overseas Solidigm listing would fall under the rules on duplicate listings, according to Seoul Economic Daily.

Abroad. MoneyToday reported that the US ordered non-essential diplomatic staff out of Saudi Arabia. The BoK named US policy after the November 3 midterms as a source of uncertainty.

What to watch next

October 27–28: US Federal Reserve meeting. The decision is due on October 28 at 18:00 UTC.
October 28: SK hynix third-quarter earnings call (Seoul Economic Daily).
Late October: Samsung Electronics' full third-quarter results. Its October 8 guidance put sales at about 195 trillion won and operating profit at about 107.40 trillion won.
Late October: the Bank of Korea's advance estimate of third-quarter GDP, one of the inputs the board named. Check the BoK release calendar for the exact date.
November 3: US midterm elections.
Early November: October consumer prices from Statistics Korea.
November 26: the next Bank of Korea rate decision.

For earlier coverage, see our October 20 South Korea brief, KOSPI after the BoK hold and Friday's early chip-led drop.

Risk checklist for readers

Concentration. Two chipmakers drive much of the KOSPI. The index can behave like a sector bet on memory chips.
Overnight links. Seoul opens after the US close, so US tech earnings and the Philadelphia Semiconductor Index often set the morning tone.
Flow data are provisional. Different outlets publish different investor-flow figures depending on the data cut. Compare them with KRX releases.
Currency effects. A stronger won raises dollar returns for foreign holders but can reduce exporters' earnings in won.
Scheduled events. Earnings calls, GDP data and central bank meetings can trigger large moves, including sidecars and circuit breakers.
Statements are not policies. Treat remarks and surveys as signals only until officials publish actual measures.

Frequently asked questions

What moves the KOSPI?

Samsung Electronics and SK hynix make up a large share of the index, so global chip demand and US tech earnings matter a lot. Foreign investor flows, the won's exchange rate, Bank of Korea policy and global bond yields also play a big role.

Why did the KOSDAQ fall more than the KOSPI this week?

The KOSDAQ lists smaller growth companies, mostly in technology, biotech and batteries, and its shares can swing more when risk appetite drops. In the week to October 23, 2026 it fell 5.42%, compared with 2.08% for the KOSPI.

What is a sidecar on the Korea Exchange?

A sidecar is a short pause in program trading orders. On the KOSPI market it is triggered when KOSPI 200 futures move 5% from the previous close and the move lasts for one minute. Program orders are then held for five minutes. One was triggered on the buy side on October 21, 2026.