They were called valves in Britain and tubes in the United States. They became transistors and then morphed into integrated circuits. Today there are hundreds or thousands of these circuits per square inch on computer chips. Here’s a documentary about the manufacturing of thermionic valves that was made by Mullard at the Blackburn factory in Great Britain. The plant was closed in the early 80’s. It seems that there was a lack of demand for their special kind of handiwork.