A thermistor is a term to indicate a product that has the properties of a resistor and is a thermal element as well. It functions based on a voltage developed across it when a fixed current is passed through it. The ambient temperature causes a change in the resistor value and accordingly, the voltage varies. Its characteristic varies according to the metal used.

Thermistors are made using oxides of metal. The metal generally used are copper, cobalt, manganese and nickel. They are made into a powder form and compressed while being subject to high temperature. There are two types of Thermistors, NTC and PTC and they are indicative of negative and positive thermal coefficient. They are generally used with measuring instruments and with protective devices.