https://en.wikipedia.org/wiki/Wax_thermostatic_element

The second sentence also fits for field effect transistors and solid state electronics in general.

In the spirit of grimdark steampunk, have you ever heard of pneumatic logic? I still see these systems operating normally in some older mechanical rooms, it’s cool to see them still working after 40-50 years.

https://en.wikipedia.org/wiki/Pneumatic_circuit

On the other hand one might as well associate it with “solar punk”, especially when powered by ambient temperature.