A thin film thermistor having a thermistor element, one pair of external leads and a metal housing is arranged such that the thermistor element is secured to the inner surface thereof by brazing. The thin film thermistor rapidly detects temperatures by means of a mechanical connection between the thermistor and an outer surface of an object that it touches. The thermistor element may be covered with a protective layer of a fired low melting point glass in order to protect the thermistor element from a severe environment.