American parts were better but became unavailable because of the war effort, cold war, space war, etc (the best parts went to the military and nasa, seconds were available that had lower quality, usually lower hfe, some so low they would have been rejected). The Japanese asked to be able to produce parts under license (US said yes, US manufacturers also said yes as they didn't care since uncle sam was buying as much as they could produce). Japanese firms started to produce american licensed solid state transistors and ics. That's why you see in early gear, american produced solid state and in later gear Japanese produced solid state(sony, toshiba, sharp, panasonic, etc).
Today, most of the japanese firms that produced solid state are either out of that side of their business or bankrupts, with a few exceptions. American firms have merged and consolidated and Intel basically won the ic market (ready to loose it again by not focusing on small chipsets for smart phones and tablets). Chinese firms are emerging but their quality sucks (unfortunately, electronic manufacturers don't seem to care that thins fail right after the warranty).
There is a whole documentary (japanese made and multiple parts) that shows many facets of the start of the Japanese electronic industry (60s to 80s) where the Japanese manufacturers admit they were clueless and had no understanding of what the americans (who were very open) were talking about and were shocked at how many solutions americans could come up with for the same problem. They were also shocked at how open american corporations were to show every part of the manufacturing process which most companies kept secret (early silicon valley folks where fairchild employees would call Motorola, and visa versa, when they had a problem, like the men going to the bathroom problem)