Micron Technology Inc. (MU) just broke a line that held for more than 17 months.

Shares fell 7.7% to about $734 in early trading Thursday. That put the stock below its 200-day moving average, which sits near $756. The last close under that level was May 30, 2025.

For the uninitiated, the 200-day average is the stock's mean price over roughly 10 months of trading. Investors watch it as the dividing line between long-term uptrends and downtrends. Crossing below it doesn't guarantee doom, but it's the kind of signal that makes people pay attention.

Micron is down 24% this week and about 40% below its June 25 record close of $1,213.56. Democratic midterm gains have raised doubts about data center buildouts. Micron also reportedly paused work on a $4.5 billion plant in Taiwan amid a labor dispute.

The pain isn't isolated. The VanEck Semiconductor ETF (SMH) is down 14.8% this week and also trades below its 200-day average. When the whole sector slips under that line, it's less about one company's bad week and more about a broader mood shift.