Seoul — August 20, 2026. Published after the market close; index and stock prices are official closing values, while currency levels reflect late-session market quotes.
The 30-second version
- The KOSPI surged 5.89% to 6,852.58 — a 381-point gain — powered almost entirely by the two semiconductor giants.
- SK Hynix jumped 12.73% after announcing a 40 trillion won (about $29 billion) share buyback-and-cancellation, the largest ever by a Korean listed company. Samsung Electronics rose 9.49%.
- Foreign investors bought a net 1.7 trillion won (roughly $1.2 billion) of KOSPI shares; local individuals and institutions sold into the strength.
- The won strengthened through the psychologically important 1,400-per-dollar line, with USD/KRW finishing around 1,394 per dollar — a gain of about 1.4% for the won and its strongest level in about 11 months.
- The KOSDAQ rose a more modest 1.99%, led by biotech on positive global vaccine news.
A record buyback lit the fuse
The single biggest catalyst was SK Hynix. The memory-chip maker said it will spend 40 trillion won — roughly $29 billion at today’s exchange rate — buying back 24.07 million of its own shares, equal to 3.3% of shares outstanding, starting August 20 and running about three months. Crucially, every share bought will be cancelled, not parked in treasury. Think of a pizza cut into fewer slices: the company’s earnings get divided among fewer shares, so each remaining share’s claim on profits grows. It is the largest buyback-and-cancellation program ever announced by a Korean listed company, and SK Hynix also raised its shareholder-return benchmark from “within 50% of cumulative free cash flow” to “50% or more” (Financial News report).
The news rippled outward. SK Hynix closed at 1,691,000 won (+12.73%), parent holding company SK Square gained 11.85%, Samsung Electronics rose 9.49% to 271,000 won — lifting its market value to about 1,584 trillion won, or roughly $1.1 trillion — while Samsung’s preferred shares added 10.07% and Samsung C&T 7.78%. Over on the KOSDAQ, biotech carried the day: Alteogen surged 11.86% on reports that BlackRock had increased its stake, ABL Bio added 3.51%, and news of Moderna’s successful phase 3 cancer-vaccine trial lifted sentiment across the sector.
Who bought, who sold — and the cracks beneath the rally
Korea’s headline daily flow data breaks out three main investor groups: foreign investors, domestic institutions, and individuals (retail). Today’s split was stark. Foreigners bought a net 1.71 trillion won of KOSPI shares, while individuals sold about 2.28 trillion won (roughly $1.6 billion) and institutions sold around 488 billion won ($350 million). These headline figures do not sum to zero — smaller participant categories outside the three main groups, such as other corporations, absorb the balance. In other words, foreigners were the only one of the three headline groups to record net buying on a 5.89% up day, while local players treated the spike as a chance to take profits. On the KOSDAQ, institutions turned small net buyers at 112.1 billion won, though foreign and retail detail for that market was not clearly confirmed in local reports.
Breadth was decent but not euphoric: 521 KOSPI stocks advanced against 338 decliners, with four names hitting limit-up (Korean exchanges cap single-day moves at 30% in either direction). The ride was rough, too — the index swung more than 300 points intraday between a low of 6,600.09 and a high of 6,904.55 before settling at 6,852. Combined turnover across both markets reached about 33.7 trillion won, or roughly $24 billion. The concentration is the real caveat: a large share of today’s gain came from just Samsung Electronics and SK Hynix, while Samsung Electro-Mechanics (+0.65%), Hyundai Motor (+0.85%) and LG Energy Solution (+0.14%) barely participated, and Hanwha Aerospace actually fell 0.85% on one of the strongest days in the index’s history.
The won broke 1,400 — a double-edged sword
USD/KRW ended the session around 1,394 per dollar, a move of roughly 1.4% in the won’s favor, taking out the 1,400 support level and marking the won’s strongest reading in about 11 months (intraday quotes were reported in the high-1,392 to 1,393 range). Two forces converged: the US Treasury’s announcement of expanded bond buybacks pulled long-term US yields lower and weakened the dollar globally, while Korean semiconductor exporters sold dollars to convert overseas revenue into won. Once 1,400 gave way, that dollar selling became self-reinforcing, according to local reporting.
A strong won cuts both ways. It flatters returns for dollar-based investors holding Korean assets and can attract further inflows. But it squeezes the won-translated earnings of exporters outside the chip complex — autos, shipbuilding and defense among them — which helps explain why those groups lagged or fell even as the index soared.
Key closing numbers
| Metric | Close | Change |
|---|---|---|
| KOSPI | 6,852.58 | +381.41 (+5.89%) |
| KOSDAQ | 840.89 | +16.43 (+1.99%) |
| USD/KRW | ~1,394 per dollar (late-session) | won up ~1.4% |
| SK Hynix | 1,691,000 won | +12.73% |
| Samsung Electronics | 271,000 won | +9.49% |
| Foreign net buying (KOSPI) | ~1.71 trillion won (~$1.2B) | |
| Individual net selling (KOSPI) | ~2.28 trillion won (~$1.6B) | |
| Institutional net selling (KOSPI) | ~488 billion won (~$350M) | |
| Combined turnover (KOSPI + KOSDAQ) | ~33.7 trillion won (~$24B) | |
What to watch next
- Foreign flows. With retail and institutions both selling, foreigners were the only one of the three headline groups on the buy side today; a reversal in foreign buying would remove the day’s clearest source of net demand.
- Buyback execution. SK Hynix’s purchases begin August 20 and run about three months — the planned buying may provide incremental demand during that window, though execution may not be uniform and offers no guarantee of price support.
- The won. Whether the self-reinforcing dollar selling below 1,400 continues, and how loudly non-chip exporters start flagging currency pressure on earnings.
- Breadth. A rally this concentrated in two chip names is fragile; watch whether autos, batteries and industrials start catching up.
- Biotech follow-through. The Alteogen stake reports and the Moderna trial news both need confirmation to sustain KOSDAQ leadership.
FAQ
Why did the KOSPI jump almost 6% on August 20, 2026?
SK Hynix announced a record 40 trillion won buyback-and-cancellation, sending it up 12.73% and Samsung Electronics up 9.49%; those two stocks did most of the lifting. Foreign investors bought a net 1.71 trillion won of KOSPI shares, absorbing heavy profit-taking by local individuals and institutions.
How big is SK Hynix’s share buyback?
40 trillion won, or about $29 billion — 24.07 million shares equal to 3.3% of shares outstanding, purchased over roughly three months from August 20 and cancelled in full. It is the largest such program by any Korean listed company.
Why did the Korean won strengthen past 1,400 per dollar?
The US Treasury’s expanded bond buybacks pushed long-term US yields down, and Korean chip exporters were simultaneously selling dollars to convert revenue. Once the 1,400 level broke, dollar selling fed on itself, and USD/KRW finished around 1,394 per dollar, its lowest level in about 11 months.
Is a strong won good or bad for Korean stocks?
Both. It boosts dollar-based returns for foreign investors and can draw inflows, but it erodes the won value of export earnings. Today that split was visible: chipmakers soared on their own catalyst while currency-sensitive names like Hyundai Motor barely rose and Hanwha Aerospace declined.
Disclaimer: This is an information and analysis publication, not investment advice. See our Methodology for data sources, standards, and our corrections policy.