Why Is the KOSPI So Volatile? Chips, Foreign Money and the Won

The KOSPI swings hard because three forces tend to hit it at the same time. Two chip companies, Samsung Electronics and SK hynix, make up about half of its market value. Foreign investors own close to half of those two companies and trade about a third of the market. And the won adds its own swing for anyone counting in dollars. All three were at work on October 13, 2026, when the KOSPI fell 5.46% to 6,035.35.

Won amounts are converted at 1,345.1 won per US dollar, the 15:30 Korea time close on October 13, 2026 (Bank of Korea, ECOS), unless another date is given.

How volatile has the KOSPI been in 2026?

These figures use the KOSPI index’s daily closes: 199 daily moves from December 16, 2025 to October 13, 2026.

• The index moved 3% or more on 65 days: 32 rises and 33 falls. That is about one trading day in three.
• It moved 5% or more on 36 days: 16 rises and 20 falls.
• The average daily move, up or down, was 2.66%.
• The largest fall was −12.06% on March 4, to 5,093.54. The largest rise was +17.91% on July 31, to 6,595.45.

The bigger picture swung just as much. The KOSPI rose 122.8% from 4,090.59 on December 15, 2025 to its peak of 9,114.55 on June 22, 2026. By October 13 it was 33.8% below that peak.

Why do Samsung Electronics and SK hynix move the whole index?

Because of their size. On October 13 the two companies made up 52.4% of the KOSPI 200 map by market value. Measured against the whole KOSPI market, worth 4,978.8 trillion won (about US$3.70 trillion) that day according to Korea Exchange (KRX) figures published by the Bank of Korea, their common shares came to about 48%.

That day Samsung Electronics fell 7.39% and SK hynix 10.09% (KRX regular-session closes). Weighted by market value at the start of the day, the 201 stocks on our KOSPI 200 map fell 5.68%. The two chip makers accounted for 4.65 percentage points of that. The other 199 stocks together fell 2.25%, and the median stock fell only 0.76%.

So a “KOSPI day” is often a chip day. Both companies are big memory-chip makers, so news about chip demand tends to move them together, and the index follows. Our comparison of Samsung and SK hynix in HBM looks at where their businesses overlap and differ.

How does foreign money move the KOSPI?

Foreign investors held 46.18% of Samsung Electronics and 49.12% of SK hynix on October 13. When they sell those two stocks heavily, the index feels it.

On October 13, by KRX’s own figures published by the Bank of Korea in ECOS (Korea Exchange trading only), foreign investors sold a net 4.59 trillion won (about US$3.41 billion) of KOSPI shares. The day before, October 12, they sold a net 2.02 trillion won (US$1.51 billion), at that day’s rate of 1,335.1.

Some broker apps also count trading on Nextrade, Korea’s alternative trading venue, so their totals can be larger. When you quote a figure, say which venues it covers.

Who is on the other side?

Mostly Korean individuals. In KRX figures for January to August 2026 (Bank of Korea, ECOS), individuals made up 39.0% of KOSPI trading by value, counting both buying and selling. Foreign investors made up 35.6%. The individual share ranged from 48.1% in January to 31.4% in July.

But the link between foreign flows and the index is loose. Our guide to how foreign investors move the KOSPI shows months when foreign investors sold heavily while the index rose.

The flow data says who sold on October 13. It does not say why, and Pacific Tape has not confirmed a cause for the falls on October 12 and 13 from a primary source.

Why does the won matter?

Foreign investors who sell Korean shares are paid in won. Taking the money home means selling won, so heavy selling can weaken the currency. A weaker won also cuts the dollar value of Korean holdings, which can prompt more selling.

The link shows up in the data, but not every day. Using the Bank of Korea’s 15:30 won-dollar closes:

• On the 33 days the KOSPI fell 3% or more, the won weakened against the dollar on 19.
• On the 32 days it rose 3% or more, the won strengthened on 25.
• The won’s average daily move against the dollar was 0.52%, about a fifth of the KOSPI’s 2.66%.

For a dollar-based investor, the currency changes the size of the swings. From December 15, 2025 to June 22, 2026 a dollar went from buying 1,471.0 won to 1,537.0, so the KOSPI’s 122.8% rise was about 113.3% in dollars. From June 22 to October 13 the won strengthened to 1,345.1, so the index’s 33.8% fall was about 24.3% in dollars. These are index-level examples, not the return of any fund.

Are there limits on how far Korean stocks can move in a day?

Yes. KRX sets three kinds.

• Daily price limit: a single stock can rise or fall at most 30% from its base price, normally the previous close. Nextrade uses the same ±30% limit, based on the KRX close.
• Circuit breakers: if the KOSPI falls 8% below the previous close for one minute, the whole market stops for 20 minutes, then reopens with a 10-minute auction. A second halt follows at 15%, and at 20% the market closes for the day (each also needs a further 1% fall from the previous trigger). They apply to falls only.
• Sidecar: if KOSPI 200 futures move 5% for one minute, program-trading orders are held for five minutes, once a day.

These rules slow sharp falls; they do not stop them. In these closes the index traded 8% or more below the previous close at some point on 10 days in the period. According to The Herald Business, the halt on June 26 was the KOSPI’s fifth circuit breaker of 2026, and Korea JoongAng Daily reported one on June 8. There is no matching halt for rises, which is how the index could close 17.91% higher on July 31.

How can I watch these forces day to day?

• Our interactive market map shows how much of the KOSPI 200 the two chip makers cover, and how the rest of the market moved.
• KRX Data Marketplace and the Bank of Korea’s ECOS publish daily KRX figures for foreign investors’ net buying. Check whether any other figure you see also counts Nextrade.
• The Bank of Korea’s ECOS publishes the won-dollar close at 15:30 Korea time, the same moment as the stock market close.

Volatility is a separate question from valuation. Why Korean shares are often said to trade at a discount, and what the government’s Corporate Value-up Program aims to change, is covered in our guide to the Korea discount.