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Weekly Market Review: Week 34 (August Week 3)

A four-session week in Korea, shortened by a substitute holiday for Liberation Day. On August 19 a spike in long-dated sovereign yields sent KOSPI down 5.80% and triggered a sell-side sidecar; board resolutions from SK Hynix for a 40.04 trillion won buyback-and-cancellation and from Samsung Electronics for up to 110 trillion won in shareholder returns then cut the weekly loss to 0.93%

HHaelangdal·Founder AnalystAugust 22, 202616 min readWeekly Review
Bottom Line

Long-dated sovereign yields set the direction this week. When the US 30-year yield reached its highest level in about two decades, a US semiconductor index fell nearly 5% on August 18 and KOSPI fell 5.80% on August 19 with a sell-side sidecar triggered. The causes cited were fiscal-soundness concerns and a surge in corporate bond issuance funding AI data-center investment. AI-linked bond issuance stood at roughly 270 billion dollars as of early July, about twice the full-year 2025 total. The AI funding structure that last week's review flagged as a risk item actually moved the index this week. The rebound came from board resolutions. Yields did not come down. SK Hynix resolved to buy back and fully cancel 40.0434 trillion won of shares, and Samsung Electronics approved 90 to 110 trillion won of 2026 shareholder returns. KOSPI's weekly loss of 0.93% is the net of a 5.80% drop and a 5.89% rebound. The same yield spike worked the other way on bitcoin. After the US Treasury doubled the size of its long-dated buyback operations, bitcoin rose 24.67%.

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Reader's Brief — 30-second TL;DR

Intermediate
Why Now

8/17 Korea closed for the Liberation Day substitute holiday, US only, S&P 500 -0.52% (7,745.06) -> 8/18 US 30-year yield at its highest in about two decades, semiconductor index down about 5%, KOSPI -1.55% (6,869.83), KOSDAQ -3.52% (834.20), foreign investors bought 790.4 billion won of SK Hynix and 177.9 billion won of Samsung for a net 86.1 billion won across the market -> 8/19 KOSPI -5.80% (6,471.17, 6,400.81 intraday), sell-side sidecar at 9:06 a.m., foreign investors sold 3.5035 trillion won and institutions 1.3244 trillion won while individuals bought 4.6367 trillion won, SK Hynix ADR -9.20%, Philadelphia Semiconductor Index -4.98% -> 8/20 confirmation of SK Hynix's 40.0434 trillion won buyback-and-full-cancellation resolution, KOSPI +5.89% (6,852.58), SK Hynix +12.73%, Samsung +9.49%, foreign net buying of 1.7117 trillion won, USDKRW down to 1,380.0 intraday for an 11-month low, Dow -1.32% on weak Walmart results -> 8/21 KOSPI +0.88% (6,912.95, down 1.35% at the open), KOSDAQ -4.63% (801.94), KOSDAQ sell-side sidecar at 10:05:05 a.m., and after the close Samsung's board approved 90 to 110 trillion won of 2026 shareholder returns

Winners ?? Losers

Up - SK Hynix +5.17% for the week (1,730,000 won, on the 40 trillion won cancellation resolution), Samsung Electronics +2.55% (281,500 won, on the 110 trillion won return resolution), Marvell +6.77%, a gold ETF +5.45%, West Texas Intermediate +5.66% (87.06 dollars a barrel), bitcoin +24.67% (78,335 dollars). Down - Nebius -21.09%, Intel -12.13%, Astera Labs -11.39%, Coherent -11.14%, Vertiv -10.85%, Walmart -10.04%, GE Vernova -10.01%, Meta -6.77%, Broadcom -6.24%, Nvidia -4.64%. Rate-sensitive long-duration growth names and AI infrastructure names fell together, and the only offsets were the two Korean memory names that announced shareholder returns.

Watch For

Reading depth

Mon 8/17 - Tue 8/18 - Korea Closed, and the US Long-End Spike

The week opened with Korea shut. Monday August 17 was a substitute public holiday for Liberation Day. August 15, Liberation Day itself, fell on a Saturday, so the next weekday was designated the substitute holiday, and the Korea Exchange closed KOSPI, KOSDAQ and KONEX. Trading and settlement through the alternative trading system were also suspended.

Monday - a session the US traded alone

The US was open. The S&P 500 fell 0.52% to 7,745.06 and the Nasdaq 0.32% to 26,644.91. The market was waiting on retailer earnings scheduled through the week: Home Depot on the 18th, Target and Lowe's on the 19th, and Walmart on the 20th.

Tuesday - the 30-year reached a two-decade high

On August 18 the US 30-year yield rose to its highest level in about two decades. Two causes were cited. One was fiscal-soundness concern tied to rising government debt. The other was the flow of data-center investment being funded through corporate bonds. AI-linked corporate bond issuance stood at roughly 270 billion dollars as of early July, about twice the full-year 2025 total.

When bond supply increases, yields rise. When yields rise, the present value of companies whose profits sit far in the future is cut first. A US semiconductor index fell nearly 5% that day. The Nasdaq closed at 26,289.71, down 1.33%.

Seoul opened after four days off and took that flow. KOSPI closed at 6,869.83, down 1.55%, and KOSDAQ at 834.20, down 3.52%. Foreign flows ran against the index, however. Foreign investors bought 790.4 billion won of SK Hynix and 177.9 billion won of Samsung Electronics while selling the rest of the market, for a net 86.1 billion won of buying. Over the five sessions from August 11 through this day, cumulative foreign net buying exceeded 8 trillion won, with most of it concentrated in those two names.

On August 18 the Seoul index fell while foreign money kept moving into the two memory names.

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This report is provided for informational purposes only and does not constitute a recommendation to buy or sell any financial instrument. Investment decisions should be made based on your own judgment and responsibility. The analysis and opinions contained herein are based on information available at the time of writing and are subject to change.

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