The answer to my question The first transistors in space: Germanium or Silicon? What about LEO? actually addressed both the first Germanium and Silicon transistor.
So now I've gotta ask about electron tubes (valves). It sounds like Sputnik-1 and Sputnik-2 had tubes, although 2 had a mix of both. But after that?
There are types of electron devices are used in RF amplifiers (e.g. klystrons, traveling wave tubes) and of course photomultiplier tubes are still being sent to space regularly (there - the ISS version is scheduled for 2020) and these could count as interesting answers, but what I'm primarily looking for is the small, compact devices like you'd find in an old radio, with the filament, grid(s) and plate all right next to each other.
The significance is that even then, transistors required so much less power than vacuum tubes because they didn't require heated cathodes (filaments) for thermionic emission of carriers. By doping a low band-gap semiconductor material, carriers could be generated at 0C rather than cherry-red hot. That meant that you could power a 1 watt transmitter with a few watts of electrical power, something sustainable with photovoltaics, and that was critical for making satellites long-lived.
Of course if you want to go to Venus, you just choose a higher band-gap semiconductor.
below: An assortment of electron tubes (vacuum tubes, valves); "Eine Zusammenstellung von Elektronenröhren." From here.