SK Hynix Shares Plunge 10% as Weak SanDisk, Western Digital Guidance Rattles Memory Chip Stocks

SEOUL — Shares of SK Hynix Inc plunged Thursday, falling 10.37%, or 173,000 won, to close at 1,495,000 won, as disappointing forward guidance from two major U.S. memory chip companies triggered a broad selloff across the global semiconductor sector and rattled South Korea's benchmark stock index.

The decline made SK Hynix, one of the world's largest producers of memory chips and a key supplier for artificial intelligence infrastructure, the worst-performing major stock within a broader selloff that briefly pushed South Korea's KOSPI index down as much as 5% during Thursday's trading session, triggering the exchange's automatic "sidecar" mechanism, which temporarily halts programmatic sell orders once futures decline sharply within a short window.

The Trigger: Disappointing US Guidance

Thursday's selloff traces directly back to earnings reports released after Wednesday's close by two major U.S. storage and memory companies, SanDisk and Western Digital. Both companies posted results that exceeded Wall Street's expectations for the quarter just completed. SanDisk reported fiscal fourth-quarter revenue that surged 372% year over year to $8.96 billion, with adjusted earnings per share of $39.25, both figures beating analyst forecasts. Western Digital similarly posted strong results, with fourth-quarter revenue climbing 44% year over year to $3.747 billion and GAAP net income surging 1,215% from a year earlier to $3.195 billion.

Despite those strong headline numbers, both companies issued forward guidance that fell short of the market's elevated expectations. SanDisk projected first-quarter fiscal 2027 revenue in a range of $10.3 billion to $10.8 billion, with a midpoint of approximately $10.55 billion, below the roughly $10.8 billion analysts had anticipated. That guidance miss, paired with a similarly underwhelming outlook from Western Digital, was enough to trigger sharp declines in both companies' shares in after-hours and premarket trading, with Western Digital falling as much as 13% to 14% and SanDisk dropping roughly 8% to 9% at various points.

A Selloff That Spread Across Asia

The disappointing U.S. guidance quickly rippled into Asian trading Thursday morning, hitting memory chip producers across the region particularly hard given their central role in the same global supply chain. Samsung Electronics, South Korea's largest company and SK Hynix's primary domestic rival, fell alongside SK Hynix, with declines ranging from roughly 5.7% to 6.3% across various points in the session. In Japan, memory chipmaker Kioxia slumped more than 10%, while broader technology indexes across the region also came under pressure, with Hong Kong's Hang Seng Tech Index falling more than 2%.

The pressure extended back to U.S. markets as well. Micron Technology, another major memory chip producer, fell more than 3% in premarket trading Thursday, while the broader Roundhill Memory ETF, which tracks a basket of memory and storage-related stocks, also declined sharply as investors reassessed valuations across the sector following the guidance misses.

A Sector Already Prone to Sharp Swings

Thursday's decline extended a pattern of extreme volatility that has characterized memory chip stocks throughout 2026. SK Hynix alone has experienced several dramatic single-session moves this year, including a 15% single-day plunge in mid-July, its largest ever at the time, after a South Korean brokerage published a second-quarter profit estimate for the company that came in 8% below consensus, citing concerns over slower-than-expected shipments of high-bandwidth memory chips used in AI applications.

That volatility has cut in both directions. Despite Thursday's steep decline, SK Hynix and its memory sector peers have posted extraordinary gains for the year overall, driven by surging demand for the high-bandwidth memory chips that power artificial intelligence data centers. SanDisk shares, for instance, had climbed as much as 640% year-to-date as of a session earlier this week, before Thursday's guidance-driven pullback, illustrating just how dramatically sentiment toward the memory sector has swung across 2026.

Analysts Divided on What Comes Next

Despite Thursday's sharp selloff, not all analysts have turned bearish on the sector's longer-term prospects. Analysts at Goldman Sachs and JPMorgan have maintained buy ratings on memory chip stocks even amid the volatility, pointing to forward price-to-earnings ratios in the range of 3.5 to 3.6 times as evidence that current valuations appear detached from the sector's underlying fundamentals. Some institutional investors have characterized the current pullback as a potential buying opportunity, provided the broader thesis around sustained AI-driven memory demand remains intact.

Other market observers have expressed more caution, noting that the sector's heightened sensitivity to even modest guidance misses reflects how aggressively investors had priced in continued exponential growth across the memory chip industry. Analysts tracking the space have noted that any performance falling even slightly below elevated market expectations has been enough to trigger rapid, outsized selloffs in recent months, a dynamic that played out again with Thursday's reaction to the SanDisk and Western Digital reports.

A Broader Test for South Korea's Market

Thursday's decline also arrived alongside separate corporate news involving SK Hynix's operations. According to a report from the Korea Economic Daily, Solidigm, a wholly owned subsidiary of SK Hynix, has formally begun a pre-IPO financing process ahead of a planned Nasdaq listing, targeting a valuation of approximately 50 trillion won, or roughly $35.15 billion, and aiming to raise between 5 trillion and 10 trillion won, or roughly $3.5 billion to $7 billion, in the process.

Even with that separate corporate development in progress, Thursday's trading was dominated by the broader memory chip selloff, which analysts characterized as reflecting sector-specific concerns tied to the pace of near-term AI memory demand rather than a systemic risk-off event across markets more broadly.

With SK Hynix and its peers continuing to exhibit some of the sharpest single-session volatility in the global technology sector this year, investors are likely to remain closely focused on upcoming earnings and guidance updates from other major memory producers, including Micron, for further signals on whether Thursday's pullback reflects a temporary reassessment or a more sustained shift in sentiment toward the artificial intelligence-driven memory chip boom that has defined much of the sector's performance throughout 2026.