Indeed, cooling would be quite bulky and require lots of extra energy. But for an environment like Venus cited (instead of small sensors), I think it should be a good option. The Carnot efficiency to cool from a Venutian environment (462C) down to 50C (reasonable chip temp) is a surprisingly good ~60%. In practice you might get 15% (? plus insulation leaking), that should still allow cooling a chip of less than ~1 watt of tdp without too much hassle inside a robot.