The optical-parts maker fell about 11% with no company news, three days after its chief executive said its products were sold out into 2029. Micron and SanDisk declined after China's top memory maker described progress on a new DRAM design.
Two of the year's strongest groups of AI hardware stocks were among the Nasdaq's sharpest decliners on Monday.
Lumentum Holdings fell about 10.8% to near $984 in early afternoon trading. On Friday, the shares touched $1,143, a record, on the same day Chief Executive Michael Hurlston said the company was "completely sold out" through early 2029. Monday's price is about 14% below that peak.
Using the roughly $86 billion market value the company carried at Friday's close of about $1,103 a share, Monday's decline equals about $9 billion. The company issued no news on Monday.
Memory makers
Micron Technology fell about 3.5% to near $993, and SanDisk lost about 6.4%. U.S.-listed shares of SK Hynix fell about 3.9%. Samsung Electronics had dropped about 4% in Seoul earlier in the day, alongside a broad decline in South Korean stocks.
The declines followed comments from ChangXin Memory Technologies, China's largest maker of DRAM chips. Company President Cao Kanyu told an industry event in Shanghai over the weekend that CXMT had made significant progress on a new memory-cell design that increases storage density, an area where Samsung, SK Hynix and Micron are also working. The target, he said, is a server memory chip using that design before the end of 2026.
The decline leaves Micron roughly 21% below the intraday record it set in June, despite strong quarterly results reported Sept. 30. Only last week, Gil Luria of D.A. Davidson lifted his target on the shares to $3,000 from $2,100, the most bullish call among Wall Street analysts.
The wider chip group
The iShares Semiconductor ETF fell about 2.5%. Nvidia lost about 1.2%, less than the group. Astera Labs, which makes connectivity chips for AI servers, fell about 5.5%. Technology, off about 1%, was the worst-performing of the S&P 500's 11 sectors.
Lumentum's run
The setup for Lumentum's decline was a long rally. The shares stood at about $153 at their 52-week low, set in October 2025. By Friday the company was valued at roughly $86 billion, supported by demand for the lasers that carry data between AI servers and an investment from Nvidia earlier this year.
Market implications
One reading is that Monday's moves were profit-taking after a crowded run. Lumentum reported no change in its business, the "sold out" comment was positive on its face, and the memory declines came on a product target rather than shipments.
A second reading is that the market is beginning to price competition and peak tightness. A Chinese producer narrowing the technology gap in server memory would challenge the pricing that has driven memory profits this year, and a sold-out order book can also mean the supply response is coming.
What to watch
ASML reports third-quarter results Wednesday and Taiwan Semiconductor Manufacturing reports Thursday. Their order commentary, along with any CXMT product timing or specifications, will show whether Monday's selling was positioning or a change in the outlook.