The most popular sensor in terms of market surveys and sales is the temperature sensor. This sensor is used in a wide range of applications critical to the medical, agricultural, industrial, and automotive communities, to name just a few. Experimental measurements clearly show that the resistance thermometers that use metals display an increase in resistance as temperature increases. The most common material used in metal thermometers is platinum. Thermometers that use semiconductors as the sensing element differ from metal-based thermometers in that the resistance decreases with increasing temperature. Thermometers that use semiconductors are thermally sensitive resistors, or what is commonly called thermistors. The semiconductors used in thermistors are not the common semiconductors such as silicon or gallium arsenide. Typically thermistors use metal oxides or combinations of metal oxides. The two commonly used thermistors are the bead type thermistor and the disc type thermistor.