GaAs (gallium arsenide) is a good choice for semiconductors -- plus you get certain speed advantages. (Back in the late 70s we thought GaAs would take over from silicon... but it never happened.) Vacuum tubes will work too, but will need much higher cathode temperatures for efficiency -- this might be overcome by adding some radioactive materials and ensuring plenty of conductive cooling at the plate. Perhaps a solder substitute for wiring could be found -- but I'm not too certain about welding instead. (Maybe D.C. can enlighten us.)
Of course, you could bypass all that and go straight to fluidic computing, with techniques known from the early 60s. A bit slower for digital computing but various analog operations could be quite efficient. (Though it might freeze up -literally- at Earth-norm temperatures.)
Other than specific sensors and such, I’m comfortable with the notion of using vacuum tube analogs for what we want to do.
To be practical, the spiderbots will need to be functional from vacuum to considerable pressure, and from space-cold to Venusian surface hot.
That means the vacuum tubes will have to have filaments, of course, and that will be a drain on the electrical system. For that reason, I think a radioactive thermionic power system would be appropriate.
In the game scenario, the unknown opposition, tentatively called the Honue, will appear to be indigenous to the surface of Venus. Clearly, their biology would be different from ours! They could be silicon based, with an emphasis on sulfur chemical reactions.
Their base of operations would be something similar to lava tubes under the surface of Venus. Initially, we wouldn’t know how many there were, or what their technological capabilities were.
Without an ability to communicate with them, and a conflict scenario from the beginning, the point of the game would be to try to figure these things out and either defeat them or learn how to communicate.