The Short Answer
The contagion did transmit. It just didn't survive the first hour.
Seoul closed sharply lower on August 6, 2026: SK Hynix −10.37%, Samsung Electronics −6.30%, KOSPI −4.58%. Those are settled closing prices. New York then took the handoff at the open — Micron opened −5.61% and traded as low as −7.41%; Seagate opened −6.88% and bottomed at −8.35%.
By 10:33 a.m. Eastern, one hour into the session and with trading still in progress, every one of those names had turned green: Micron +0.38%, Seagate +1.65%, SOXX +1.51%, AMD +1.21%.
At that moment only two stocks in the entire complex were still down more than 1%. They happen to be the only two that had just reported earnings.
Read This Before the Numbers
This article mixes two different kinds of time windows. They are not interchangeable and must not be subtracted from one another:
| Data | Status | Timestamp |
|---|---|---|
| Korean equities | Settled closing prices | Korea close, 2026-08-06 |
| US equities | Intraday, session in progress | 10:33 a.m. ET, 2026-08-06 (hour 1) |
Korean figures were independently re-verified against KRX price data. US figures were pulled live at the time of writing and are not closing prices. The first hour after the open is the most volatile stretch of the trading day, and every US reading below can change by the close.
Because the two sides cover different window lengths — a full Korean session versus a single US hour — this article deliberately does not compute any "US versus Korea spread." That subtraction is invalid when the windows don't match.
Seoul: The Part That Has Settled
| Instrument | Close | Change |
|---|---|---|
| SK Hynix (000660) | ₩1,495,000 | −10.37% |
| Samsung Electronics (005930) | ₩230,500 | −6.30% |
| KOSPI Index | 6,296.38 | −4.58% |
The decline is real and final, and it sorted by proximity to high-bandwidth memory: the closer a company sits to HBM, the harder it fell.
New York: The Open Followed, Then Reversed
Every US figure below comes from the same moment in the same session, so these names are directly comparable with one another.
| Instrument | At open | Session low | At 10:33 ET | Rebound off low |
|---|---|---|---|---|
| Seagate STX | −6.88% | −8.35% | +1.65% | +10.0pp |
| SOXX (semis ETF) | −1.54% | −2.69% | +1.51% | +4.2pp |
| Broadcom AVGO | +0.54% | −1.80% | +1.38% | +3.2pp |
| SMH (semis ETF) | −0.81% | −1.78% | +1.36% | +3.1pp |
| Texas Instruments TXN | −1.10% | −1.83% | +1.35% | +3.2pp |
| AMD | −2.26% | −2.60% | +1.21% | +3.8pp |
| Micron MU | −5.61% | −7.41% | +0.38% | +7.8pp |
| Nvidia NVDA | +1.05% | −0.02% | +0.12% | +0.1pp |
| S&P 500 SPY | +0.04% | −0.09% | +0.07% | +0.2pp |
| Nasdaq 100 QQQ | −0.91% | −1.23% | −0.02% | +1.2pp |
| Intel INTC | −2.81% | −5.40% | −0.13% | +5.3pp |
| SanDisk SNDK | −13.21% | −13.88% | −6.34% | +7.5pp |
| Western Digital WDC | −17.39% | −21.51% | −11.35% | +10.2pp |
What stands out:
- Micron opened down 5.6%, traded down 7.4%, and was positive an hour later. That is a full sequence of absorbing the Korean move and rejecting it.
- The rebound was universal. Even Western Digital, the worst performer of the day, recovered 10.2 percentage points off its low — the largest bounce in the table. It simply started from a far deeper hole.
- Only SanDisk and Western Digital remained down more than 1%.
The Central Puzzle: Western Digital Beat on Everything, Guided Margins Higher, and Fell the Most
From Western Digital's official earnings release dated August 5, 2026 (investor.wdc.com):
Fiscal Q4 2026 actuals
| Metric | Result | Versus guidance |
|---|---|---|
| Revenue | $3.747B | +44% year over year, above company guidance |
| Non-GAAP gross margin | 54.4% | Above guidance |
| Non-GAAP EPS | $3.56 | Above guidance |
Fiscal Q1 2027 guidance
| Metric | Guidance |
|---|---|
| Revenue | $4.1B ± $0.1B |
| Non-GAAP gross margin | 55–56% (still expanding) |
| Non-GAAP EPS | $4.00 |
Three actuals above its own guidance, and gross margin guided higher for the coming quarter. The stock opened down 17.4% and sat at −11.35% an hour into the session.
SanDisk's setup was similar but milder: a large beat on both revenue and EPS, paired with next-quarter revenue guidance that landed roughly in line with consensus rather than above it.
Why this rules out a demand explanation: Seagate and Western Digital sell into the same hard-drive end market. Seagate did not report this week and is +1.65% today. Western Digital did report and is −11.35%. Same end market, same day, same trading hour, opposite directions. The difference is not the industry — it is which company just held a call.
What is being repriced is not the fundamentals of storage. It is the positioning in these particular stocks.
The "Parabolic Run, Now Profit-Taking" Story Only Works at a One-Week Window
This is the part worth keeping.
Nearly every explanation of today's move will say these names had run too far and are giving it back. Check the past week and that looks airtight. Extend the window and it inverts.
All figures below are through the August 5 close — settled, and excluding today:
| Instrument | 1 week | 1 month | Since June 1 |
|---|---|---|---|
| SanDisk SNDK | +32.9% | −16.5% | −23.3% |
| Micron MU | +20.9% | −4.8% | −13.7% |
| SOXX | +14.1% | −3.8% | −7.2% |
| SMH | +13.0% | −2.0% | −6.3% |
| Western Digital WDC | +12.4% | −2.4% | −4.9% |
| Seagate STX | +9.6% | +1.2% | −9.0% |
| Nasdaq 100 QQQ | +8.4% | +1.1% | −3.3% |
| S&P 500 SPY | +5.5% | +3.0% | +1.7% |
At one week: SanDisk +32.9%, Micron +20.9%. Textbook parabolic top.
At one month: SanDisk −16.5%, Micron −4.8%, Western Digital −2.4% — while the S&P gained 3.0%.
These stocks did not rise over the past month. They lagged the index and lost ground. The "surge" was a rebound off a deeper drawdown, recovering what they had already given up.
So the accurate description is not "they went up too much, now they fall." It is this: a group of very high-amplitude stocks that has gone nowhere, or backwards, for a month. Anyone citing "+20.9% in a week" as the explanation has selected the window that makes the story tidy.
Three Reasons This Is Not Systemic Risk
| Check | Reading | Interpretation |
|---|---|---|
| VIX | ~15.5, below 16.50 on Aug 4 and 15.81 on Aug 5 | Volatility fell rather than spiked; no panic being priced |
| S&P / Nasdaq | SPY +0.07%, QQQ −0.02% | The broad market barely moved |
| Sector breadth | AMD, Broadcom, TI, SOXX, SMH all green | Semiconductors as a group are up, not down together |
A genuine market-wide de-risking would show rising volatility, a visibly lower index, and broad semiconductor weakness. None of the three is present.
What to Watch Next
- The US closing print. This is an hour-one reading. Whether today's reversal holds into the close is the only real test of whether the rejection was genuine.
- Seoul's next open. Either Korea found its own floor, or it repairs upward toward New York's bounce.
- Whether Western Digital and SanDisk narrow their losses. If a company with expanding gross margins keeps getting sold, the pressure is coming from positioning rather than from any judgment about value.
Limitations
- All US figures are intraday prices as of 10:33 a.m. ET on 2026-08-06. The session had not closed. Closing data may differ.
- Korean figures are settled closing prices, independently re-verified.
- This article covers public market data and publicly disclosed earnings only. It contains no position or trading information.
- SanDisk's specific next-quarter guidance figure comes from post-call market commentary rather than the company's own release, so it is described qualitatively here and no dollar amount is quoted.