Resistivity is a property of a material, measured in Ωm, defined as the product of the resistance of a component made of the material and its cross sectional area divided by its length at a given temperature.
- Good conductors have a very low resistivity (in the order of 10-8 Ωm), insulators have a value in the order of 1016 Ωm, and semiconductors have values between these extremes.
- Resistivity in metals and semiconductors generally increases with temperature.
The negative temperature coefficient (NTC) thermistor is an electrical component made from a semiconductor whose resistance falls with temperature (because the number density of charge carriers increases).