The average temperature of deep space is approximately -270.45°C or 2.73 Kelvin), which is just above absolute zero. This baseline temperature is set by the Cosmic Microwave Background (CMB) radiatio...
Which is absolute nonsense, because vacuum has no temperature.
If you had a thermometer that had no heat generation then yes.
If you have a resistor or other heat generating circuit then you need to have the needed surface area to radiate the heat away. If you don't, it will heat up. It's a rate problem.