A thermally reactive device which becomes highly resistive at a specific temperature or current.

An increase in resistance due to an increase in temperature.

A PTC thermistor is one whose zero-power resistance increases with an increase in temperature.

Positive Temperature Coefficient (PTC) refers to materials that experience an increase in electrical resistance when their temperature is raised. Materials which have useful engineering applications usually show a relatively rapid increase with temperature, i.e. a higher coefficient. The higher the coefficient, the greater an increase in electrical resistance for a given temperature increase.