feast your ocular orbs on this cross section of a miniature Nuvistor vacuum tube.
RCA published a really nice cutaway drawing with annotations.
and here is the Nuvistor, flanked by a "miniature" vacuum tube on the left and a transistor from the same era on the right. RCA's Nuvistor was just a micro-miniaturized vacuum tube they felt could beat the transistor. (it did not.)
@tubetime I'd never heard of these until a recent YT video by 8-bit Guy. I don't even remember seeing them in the electronics I poked around in when I was a kid. I guess they were pretty spendy to make as they hadn't had a chance to scale production much, so they didn't make it into a lot of stuff. But, wow, what a cool lil dude. If semiconductors weren't a thing, we could've eventually had Pip Boys instead of smart phones (probably wouldn't have been very "smart" though).