Hi @gabagabado
Chances are that the temp sensor is inbuilt the GPU chip itself.
CPU's have a built in thermocouple that senses the core temp of the CPU so no doubt GPUs are the same.
If it's getting too warm it could be due to faulty drivers or vram causing the GPU to work harder than it should.
No doubt the fans on the card will also have temp sensors (thermistors) in them as well.
Are the fans on high speed when the temp rises?