Key Silicon Valley companies like Fairchild and Hewlett-Packard were founded during the highly restrictive immigration policy that prevailed between the 1924 Johnson-Reed Act and the 1965 Hart-Cellar Act. Intel was founded just a few years after. A lot of golden age Silicon Valley companies were founded around or shortly after 1970, when the U.S. foreign-born population hit the lowest point in American history, under 5%.
Of course, even during that period, we allowed in German scientists, leading professors, etc. It's a handful of people. The highly selective immigration policy that prevailed from 1924-1965 is likely a key reason why so many Silicon Valley companies were founded by immigrants. That has very little to do with this story, which is about reversing mass immigration.