KOSPI Plunge on Oct. 13: Timeline, Sidecar vs Circuit Breaker, and KOSDAQ

South Korea's KOSPI fell more than 6% on Oct. 13, set off its first sell-side sidecar since Aug. 19 and slipped below 6,000. Here is the day hour by hour, what a sidecar is, why no circuit breaker hit, and how far the index sits below June's record.

South Korea’s main stock index tumbled on Tuesday, Oct. 13, dropping more than 6% by late morning, KED Global reported, and setting off the market’s first sell-side sidecar since Aug. 19. The KOSPI plunge was led by memory-chip giants Samsung Electronics and SK hynix, and SBS counted it as the fifth losing session in a row.

Where it stands: At 3 p.m. Korea time (KST), the KOSPI was at 6,007.37, down 5.98% on the day, The Korea Herald’s Investor reported. Trading ends at 3:30 p.m.; at the time of writing, none of the outlets we checked had reported the official close, so every Tuesday figure below is an intraday reading tied to a time and an outlet.

The KOSPI (Korea Composite Stock Price Index) tracks the main board of the Korea Exchange. Here is the day in order, and what the trading pause did and did not mean.

The KOSPI plunge, hour by hour

The index opened at 6,186.08, down 3.10% from Monday’s close of 6,384.24, and kept sliding. Each reading below comes from the outlet that reported it:

When (KST) KOSPI and change Outlet
09:00 open 6,186.08 (-3.10%) The Herald Business
09:20 6,113.24 (-4.24%) The Asia Business Daily
09:47 Sidecar: program selling paused The Herald Business
09:55 6,057.55 (-5.12%) The Herald Business
10:40 5,996.16 (-6.08%), under 6,000 Seoul Economic Daily
11:08 5,989.18 (-6.19%) SBS News
Around midday 5,914.35 (-7.4%) Associated Press
13:00 5,976.34 (-6.39%) SBS News
15:00 6,007.37 (-5.98%) The Investor (Korea Herald)

Outlets did not agree on how deep the low went. SBS, citing exchange data, said the day’s bottom by 11:08 a.m. was 5,950.00, a 6.80% drop. AP’s midday report, at 5,914.35 and down 7.4%, was deeper still and the lowest since late July by AP’s reckoning. The 3 p.m. Korea Herald story named a shallower low, 5,974.03 around noon. Each figure belongs to its outlet, and they do not reconcile. SBS also said the index fell below 6,000 for the first time since July 31.

A five-session slide from 7,003.74

Tuesday’s drop capped a fast reversal. SBS reported that the KOSPI closed at 7,003.74 on Oct. 2, back above 7,000 at the close for the first time since late September, and then fell every session after that. Financial News (fnnews) listed the daily losses: 0.89% on Oct. 6, 1.98% on Oct. 7, 2.62% on Oct. 8 and 3.65% on Oct. 12. There was no trading on Oct. 9, a public holiday, or over the weekend that followed.

By 11:08 a.m. on Tuesday, SBS put the cumulative loss since Oct. 2 at 1,014.56 points, or 14.49%. SBS added that a lower close on Tuesday would make this the first five-day losing run since the stretch from Dec. 24, 2024, to Jan. 2, 2025.

Sidecar vs circuit breaker: what the pause did and did not do

A sidecar slows down one kind of trading. A circuit breaker stops all of it. Tuesday had the first, not the second.

The sidecar. Program trading means computer-driven orders that funds send in large baskets, often tied to futures. Korea Exchange’s own trading guide says a KOSPI sidecar triggers when the price of KOSPI 200 futures (contracts tied to an index of 200 major KOSPI stocks) moves 5% or more from its base price and stays there for one minute. On a fall, sell orders from program trading are suspended for five minutes. It can fire only once a day and not before 9:05 a.m. Ordinary buying and selling of shares continues, as Korea JoongAng Daily explained when one fired in July.

The trigger came at 9:47:58 a.m. on Tuesday, The Herald Business reported: KOSPI 200 futures had dropped 5.08% to 955.02, measured against a base price of 1,006.22. No sell-side sidecar had fired since Aug. 19, and none of either kind since Aug. 20. By fnnews’ count it was sidecar No. 50 on the KOSPI this year, 26 of them on the sell side. By July, JoongAng had reported, the year’s combined count already topped the old annual record of 26, set during the 2008 financial crisis.

The circuit breaker. This one watches the KOSPI index itself, not futures. Under the KRX guide, phase one triggers when the index falls 8% or more from the previous day for one minute. Trading in every stock then halts for 20 minutes, with only order cancellations allowed, and it restarts through a 10-minute single-price auction, where orders are pooled and matched at one price. Phase two kicks in at a 15% fall, and phase three, at 20%, closes the market for the rest of the day.

Sidecar Circuit breaker
Trigger KOSPI 200 futures move 5% from base for one minute KOSPI index down 8% from prior day for one minute
What stops Program-trading orders only All trading
How long Five minutes 20 minutes, then a 10-minute single-price auction
Bigger steps None; once a day 15% phase two; 20% closes the market
On Oct. 13 Yes, sell-side No

Tuesday’s worst reported drop, AP’s 7.4%, stayed short of the 8% line, so no circuit breaker fired.

The last time it went further: July 28

The most recent circuit breaker came on July 28. The Korea Times reported that the breaker tripped at 10:14 a.m. and froze trading in KOSPI shares for 20 minutes; the index ended that day 10.84% lower at 6023.63. The Korea Times also cited CXMT’s blockbuster Shanghai stock market debut the day before as a factor, the same Chinese memory maker that was in the headlines again this week.

Samsung, SK hynix and who did the selling

Two companies carry an outsized share of this index. Samsung Electronics and SK hynix account for nearly half the value of everything listed on the KOSPI, SBS said, so when they fall the whole index falls with them. As of 3 p.m., The Korea Herald reported Samsung down 5.99% and SK hynix down 8.79%. The paper said the rout had wiped more than 800 trillion won off the market’s value, which it converted to $595.5 billion, leaving the total under 5,000 trillion won.

Foreign investors were the main sellers. The Korea Herald’s 3 p.m. story put their net selling for the day at 2.2 trillion won. Local buyers took the other side: Seoul Economic Daily’s 10:40 a.m. tally showed individuals had bought a net 1.05 trillion won, with institutions adding 598.7 billion won. Net selling means a group sold more shares than it bought. For the bigger picture, see our look at the foreign selling behind it.

KOSDAQ, the won and the fear index

KOSDAQ, Korea’s second, more tech-heavy board, opened down 3.00% at 823.69, The Herald Business reported. Seoul Economic Daily had it at 811.49, down 4.44%, by 10:40 a.m., and SBS put it at 818.60, down 3.6%, at 1 p.m.

The won barely moved early on. Korea JoongAng Daily, carrying Yonhap, said it weakened by 0.1 won to 1,335.70 per US dollar in early trade, against a 3:30 p.m. Monday quote of 1,335.1. A higher number means a weaker won.

The VKOSPI, which SBS described as Korea’s fear index, measures how big a price swing traders expect. At 1 p.m. it stood at 50.24, up 23.35% from Monday, SBS said. That was its largest one-day jump since March 4.

Elsewhere in Asia, and the reasons outlets gave

Korea fell much harder than its neighbors. In its midday report, AP had Japan’s Nikkei 225 down 2.5% at 67,292.39, Taiwan’s Taiex down 1.9%, Hong Kong’s Hang Seng down 1% at 24,033.51, the Shanghai Composite down 1.1% and Australia’s S&P/ASX 200 down 0.2%. We had not seen closing levels for those markets at the time of writing.

Outlets named several causes, not one:

  • Chinese competition. CXMT said it plans a denser kind of server memory by the end of 2026. Its claims remain unverified, and it has not shared yields or customers.
  • US chip stocks. The night before, Nvidia fell 1.3%, Micron 3.9% and the Philadelphia Semiconductor Index 2.67%, The Korea Herald reported. See what happened to Micron in New York.
  • AI-spending doubts. SBS cited an early-October media report putting OpenAI’s annualized revenue at $50 billion, short of the $68 billion to $70 billion the market expected. It later proved to be a difference in how revenue was counted, not a fall in sales, SBS noted. More in the OpenAI revenue report that hit AI stocks.
  • Buybacks ending. Kiwoom Securities’ Han Ji-young told The Herald Business that with the buyback “which had served as a supply-demand buffer” winding down, the market had less ability to absorb selling.
  • Oil and the Middle East. SBS cited a Houthi attack on a Saudi airport and higher oil prices. AP’s midday snapshot, though, had Brent crude down 1.4% at $105.20 a barrel.

Why chip news moves this index so much comes down to what Samsung and SK hynix sell; how different kinds of memory demand affect chip stocks covers that.

How far below the June record

SBS put its intraday record at 9,385.59 on June 19, and Korea JoongAng Daily reported a record close of 9,114.55 on June 22. By our arithmetic, the 3 p.m. reading of 6,007.37 was roughly a third below that June 22 close and more than a third below the intraday peak.

The year as a whole still looks very different. As of Monday’s close, before Tuesday’s drop, The Korea Herald said the KOSPI was up 51% in 2026, while Taiwan’s market had gained more than 70%.

Frequently Asked Questions

Why did the KOSPI plunge on Oct. 13?

Outlets pointed to several things at once: Chinese memory maker CXMT’s plan for denser server DRAM, a 2.67% fall in the Philadelphia Semiconductor Index the night before, heavy foreign selling, the end of share buybacks that had been supporting prices, and Middle East tensions. No single cause explains the whole drop.

What is a sidecar on the Korean stock market?

A sidecar is a five-minute pause in program trading, the computer-driven orders big funds send in bulk. Under Korea Exchange rules it kicks in after KOSPI 200 futures rise or fall at least 5% from their base price and hold there for a minute. Regular buying and selling keeps going.

Did a circuit breaker trigger on Oct. 13?

No. A circuit breaker requires an 8% drop in the KOSPI index itself versus the prior close, lasting one minute. The deepest intraday reading reported, by AP, was a 7.4% fall. The last circuit breaker was on July 28.

How far is the KOSPI below its record?

SBS put the intraday record at 9,385.59 on June 19, and JoongAng Daily reported a record close of 9,114.55 on June 22. At 3 p.m. on Oct. 13 the index was at 6,007.37, roughly a third below that record close by our arithmetic.

What is the VKOSPI?

The VKOSPI is Korea’s fear index, a gauge of how big the price swings traders expect are. SBS reported it at 50.24 at 1 p.m. on Oct. 13, up 23.35% from the previous session.

Sources

This article is for general information only and is not investment, tax or legal advice. Life Stonks does not recommend buying or selling any security, and nothing here predicts what any market or stock will do. Intraday market figures change through the trading day; the times and sources are given where each figure appears. Talk to a licensed professional before making a financial decision.