Someone discovered that a 3-terminal semiconductor device could be built using copper oxide as a semiconductor in the 1920s.  But copper oxide is a lousy semiconductor, and it was a lousy transistor. So it was just an interesting lab phenomenon. It wasn&#x27;t until Bell Labs finally figured out the physics behind semiconduction in the 1950s that transistors really worked.<p>But suppose someone like Edison had gotten hold of the 1920s transistor lab experiment and tried to make it better by trying many different materials.  (That&#x27;s how he got a usable, cheap light bulb filament; thousands of materials were tried, ending with carbonized paper.)  They would have tried selenium (selenium rectifiers were known) and galena crystals (crystal radios were known). They probably would have gotten a point-contact transistor out of galena, which would have led to germanium. It would have been unreliable and heat-sensitive until germanium purification was figured out.  They might have tried grey tin, which is a semiconductor but a dead end.  They probably wouldn&#x27;t have tried silicon, because you have to grow silicon crystals first, which is hard and wasn&#x27;t done until 1950.<p>So a transistor radio might have been demoed by 1930 or so.