First, people are buying equities in general because interest rates are being held low artificially by the Fed, which has been pressured by the President to do this.
Second, few traders and investors understand how to differentiate semiconductor companies, so when it blows, it will all blow. People get out of crowded trades chaotically. Investors and traders, who are largely unsophisticated about the specific technologies that each company develops and markets, will punish the sector rather than choosing individual names to sell. I will say it again: most people who trade tech professionally have no fucking clue what these companies actually build. They look at numbers, watch earnings reports, and listen to buzzword-laden commentary from research analysts.
Look at Apple. Their supply chain is threatened by factory shutdowns and a huge market of theirs has basically been put on ice, but their stock is near all-time highs. They haven't made a game-changing product since the days of Steve Jobs, and people usually say their value now comes from their execution. But how can you execute if your suppliers are shut down and one of your major markets is closed for business?
INTC is facing tons of pressure in enterprise and PC from AMD, their 10nm has been a disaster for them, and yet their stock popped 9% on earnings due to cloud demand. It's trading near dot-com bubble levels. They are getting hurt in their competition vs TSMC on fab, and losing market share to AMD, yet their stock is like a rocket ship. Doesn't this seem weird?
QCOM has been hit hard by several regulators and in a number of lawsuits for its IP bullying, it has come out and said that coronavirus is going to hurt smartphone manufacturing and sales, and yet its stock is trading near all-time highs.
Don't ever confuse stock performance with company performance. Boeing stock is trading at more than double where it was when the 737 Max 8 took its first flight four years ago.