64.KOSPI Jumps 3.56% on KRW 2.1T Foreign Buying — SK hynix Leads, but Market Breadth Stays Weak

Market date: August 13, 2026 · Based on the KRX regular-session close

Key question: Foreign investors bought about KRW 2.12 trillion of KOSPI cash equities and the index jumped 3.56%. Did that mean the rally finally became broad-based?

Key answer: Not yet. Foreign-buying concentration in Samsung Electronics common shares and SK hynix fell sharply from the previous session, but KOSPI still had more declining stocks than advancing stocks. The money became less concentrated by amount; market participation remained narrow.

KOSPI 6,813.34 +3.56%

KOSPI 200 1,071.24 +4.06%

KOSDAQ 861.37 +0.29%

Foreign KOSPI Net Buying About KRW 2.12tn Cash equities

SK hynix Foreign Flow +KRW 1.0551tn Stock +5.92%

KOSPI Breadth 333 up / 531 down 34 unchanged

Takeaway: KOSPI rose strongly while declining stocks outnumbered advancing stocks. August 13 was stronger than a simple two-stock semiconductor rally, but the price advance was still dominated by large-cap performance.

In this article

Why the KOSPI could jump despite weak breadth
Where the foreign money went
August 12 vs. August 13 concentration
Why lower concentration did not mean broad participation
Cash buying, futures selling and program flows
Why KOSDAQ did not confirm the move
What to watch next
FAQ

South Korea's KOSPI jumped 3.56% to 6,813.34 on August 13, while foreign investors bought about KRW 2.12 trillion of KOSPI cash equities. But the headline numbers hide an important split.

More than KRW 1 trillion of foreign net buying went into SK hynix Inc. (KRX: 000660), while Samsung Electronics Co., Ltd. (KRX: 005930) recorded foreign net selling. At the same time, 531 KOSPI stocks declined while only 333 advanced.

That makes August 13 a useful example of the difference between lower foreign-buying concentration by value and a genuinely broad-based market rally.

Why could the KOSPI jump 3.56% while most stocks fell?

The KOSPI is a market-capitalization-weighted index. Large companies therefore have much more influence on the index than smaller constituents.

This helps explain an otherwise unusual-looking session. The KOSPI rose 3.56%, while the KOSPI 200 gained an even stronger 4.06% to 1,071.24. By contrast, the KOSDAQ rose just 0.29% to 861.37.

Headline index
KOSPI +3.56%
KOSPI 200 +4.06%

≠

Market participation
333 KOSPI advancers
531 KOSPI decliners

In market terminology, breadth measures how many stocks are participating in a rise or decline. A capitalization-weighted index can surge even when most stocks are falling if a relatively small group of heavyweight companies performs strongly.

For more on this index structure, see how mega-cap stocks can move the KOSPI.

Where did the foreign money go?

Foreign investors as a category bought about KRW 2.12 trillion of KOSPI cash equities on August 13.

The most striking stock-level figure was SK hynix. Foreign net buying in SK hynix reached KRW 1.0551 trillion, while the stock climbed 5.92% to KRW 1,593,000.

Samsung Electronics also rose sharply, gaining 4.89% to KRW 268,000, but its foreign flow went in the opposite direction. Foreign investors recorded approximately KRW 98.0 billion of net selling in Samsung Electronics common shares.

They also sold about KRW 99.4 billion of Samsung Electronics preferred shares, separately listed on the Korea Exchange under ticker 005935.

Interpretation limit: These figures do not show that one identifiable group of foreign investors sold Samsung Electronics and transferred the proceeds directly into SK hynix. The foreign-investor category aggregates many institutions, funds, brokers and strategies.

From 82.1% concentration to about 45%

The comparison with August 12 makes the change clearer.

Foreign-flow measure	August 12	August 13
Total foreign KOSPI net buying	KRW 2.8429tn	About KRW 2.12tn
Samsung Electronics common	+KRW 1.4816tn	-KRW 98.0bn
SK hynix	+KRW 852.2bn	+KRW 1.0551tn
Samsung common + SK hynix share of total foreign buying	82.1%	About 45%

On August 12, Samsung Electronics common shares and SK hynix together represented about 82.1% of total reported foreign KOSPI net buying.

On August 13, SK hynix's KRW 1.0551 trillion of foreign buying minus Samsung Electronics' KRW 98.0 billion of foreign selling produced a combined net contribution of roughly KRW 957 billion, or about 45% of total reported foreign KOSPI net buying.

Including Samsung Electronics preferred shares, the three securities contributed about KRW 858 billion on a net basis. The resulting calculated residual was roughly KRW 1.26 trillion outside those three securities.

Important: The KRW 1.26 trillion figure is a calculated residual, not an exchange-reported distribution category. It does not show that the amount was spread evenly across hundreds of other KOSPI stocks. Several additional large-cap purchases could produce a large residual without improving overall market breadth.

For the previous session's concentration structure, see August 12 foreign-buying concentration.

Why lower concentration did not mean broader market breadth

August 13 produced two different forms of evidence.

Foreign-buying concentration declined by amount. Samsung Electronics common shares and SK hynix accounted for a much smaller percentage of total foreign net buying than one day earlier.

Price participation remained weak. KOSPI still had substantially more declining stocks than advancing stocks.

The central distinction: Less concentration of foreign net buying by amount is not the same as broad market participation.

The session was therefore stronger than a two-stock semiconductor story, but the rally itself remained dominated by heavyweight performance.

Why spot buying and futures selling can happen together

Another apparent contradiction appeared in derivatives. Foreign investors bought about KRW 2.12 trillion of KOSPI cash equities but sold approximately KRW 344.3 billion of KOSPI 200 futures.

That combination is not automatically bearish. Index futures can be used for outright market exposure, hedging, relative-value positions, execution strategies or portfolio adjustments. The investors behind futures transactions also do not have to be the same investors buying individual stocks.

Illustrative scenario: A fund could increase holdings in selected Korean companies while selling index futures to reduce short-term exposure to a broader market decline. This is an example of how the instruments can be used, not an explanation of the actual August 13 trades.

August 13 was also the last trading day for the August monthly KOSPI 200 options, although it was not the expiry of the regular September KOSPI 200 futures contract. Expiry-related hedging or position adjustments may therefore have influenced derivatives activity, but the available data do not establish that this caused the foreign futures selling.

For more background, see how KOSPI cash and futures flows can diverge.

Program trading also provided less confirmation than the previous session. Non-arbitrage program flows moved from roughly KRW 404–406 billion of net buying on August 12 to about KRW 67 billion of net selling on August 13.

Why KOSDAQ did not confirm a broad Korean risk-on move

KOSDAQ strengthened only 0.29%, far less than the KOSPI or KOSPI 200.

Foreign investors sold about KRW 138 billion of KOSDAQ stocks, while institutions sold approximately KRW 116 billion. Individuals were net buyers.

Breadth was also weak: 629 stocks advanced and 996 declined, with 81 unchanged.

KOSDAQ does not have to rally every time the KOSPI rises. But if the question is whether risk appetite was expanding across the Korean equity market, KOSDAQ did not provide that confirmation on August 13.

What the August 13 pre-market thesis got right — and wrong

The pre-market question was whether the semiconductor-led rally could expand beyond Samsung Electronics and SK hynix.

The close produced a mixed scorecard. Foreign cash buying remained very strong, SK hynix retained major foreign demand, and the percentage of total foreign buying accounted for by Samsung Electronics common shares plus SK hynix fell sharply.

But several broader confirmation signals were absent. KOSPI breadth remained negative, foreign investors continued to sell KOSPI 200 futures, non-arbitrage program flows turned negative, and foreign and institutional investors sold KOSDAQ stocks.

The morning thesis was therefore partly supported on foreign-flow concentration, but it was too early to declare market-wide participation.

The original framework is available in the August 13 pre-market broadening test.

What to watch next

The next session should test whether August 13's lower concentration by amount is followed by stronger participation across the market.

U.S. semiconductor performance
U.S. Treasury yields
USD/KRW
Foreign flows in Samsung Electronics and SK hynix
KOSPI 200 futures positioning
KOSPI market breadth
KOSDAQ foreign and institutional flows

One timing point is particularly important. The July U.S. Producer Price Index was released at 21:30 KST on August 13, about six hours after the KRX regular session closed at 15:30.

It therefore cannot explain the August 13 KOSPI rally. Its relevance begins with the following trading session through its potential impact on U.S. yields, the dollar, semiconductor stocks and broader risk sentiment.

Bottom line

August 13 was stronger than a simple two-stock semiconductor rally, but it was not yet a broad Korean equity rally.

Foreign-buying concentration in Samsung Electronics common shares and SK hynix fell from about 82.1% on August 12 to about 45% on August 13. That shows that their share of reported foreign net buying declined substantially by value.

But declining KOSPI stocks still outnumbered advancing stocks, KOSDAQ participation remained weak, foreign investors sold KOSPI 200 futures, and non-arbitrage program flows did not confirm the cash-equity surge.

Foreign net buying became less concentrated by amount, but the market rally had not yet broadened by participation.

FAQ

How can foreigners buy KRW 2.1 trillion of KOSPI stocks while selling Samsung Electronics?

The foreign-investor figure aggregates transactions across KOSPI securities and investors classified as foreign. The category can record net selling in Samsung Electronics while buying larger amounts of SK hynix and other KOSPI stocks. It does not imply that the same investors made both trades.

Why can the KOSPI rise more than 3% when more stocks fall than rise?

KOSPI is market-capitalization weighted. Large companies have much greater influence on the index than smaller constituents, so strong gains in heavyweight stocks can outweigh declines across a larger number of smaller stocks.

Does heavy SK hynix buying prove foreign investors are more bullish on its HBM outlook?

No. SK hynix has verified exposure to HBM and AI-server memory, but one day of aggregate foreign net buying does not establish long-term conviction, competitive preference or an industry view shared by all foreign investors.

Is foreign spot buying combined with futures selling bearish?

Not necessarily. Index futures can be used for hedging, relative-value trades, execution or directional positioning, and different investors may be responsible for the cash and futures transactions. August 13's options last-trading-day context adds another reason to avoid a simple bearish interpretation.

Why does KOSDAQ matter when judging whether a Korean rally is broadening?

KOSDAQ provides a useful cross-market check because it has greater exposure to smaller and growth-oriented companies than KOSPI. Its weak performance, negative foreign and institutional flows, and negative breadth on August 13 suggested that risk appetite had not spread broadly across Korean equities.

Can option-expiration flows predict the next trading day?

Not reliably. Expiration sessions may contain temporary hedging, position closing and relative-value activity. Futures and options flows should therefore be reassessed in the following session rather than treated as a standalone directional forecast.

Sources

Investment Disclaimer: This article is based on publicly available information and is intended for market and company analysis only. It does not constitute investment advice or a recommendation to buy or sell any security. All investment decisions and risks remain the responsibility of the investor.

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