According to William Beaty
The transistor was invented around 1923, by physicist Dr. J. Edgar Lilienfeld, the father of the modern electrolytic capacitor. WHAT?!!! But everyone knows that it was invented at Bell Labs in 1947. Nope. The original transistor was a 1920s thin-film device deposited on glass. […] Dr. Lilienfeld also built MOSFETs using the natural oxide layer found on aluminum plates. He also built a working transistor radio and showed it around to various companies. It was ignored, possibly because he didn’t have a solid theory to explain how his invention worked, but more probably because it was weird and new.
For example, here’s a patent he filed in 1926.