Abstract: An improved radiation detector is provided which comprises a thick film of thermistor material deposited upon a substrate of beryllium oxide, alumina or other suitable material having high thermal conductivity. The substrate is soldered to and supported by a heat sink. The detector films of this invention may be deposited in pairs, one element of each pair being shielded, to compensate for temperature fluctuations. An array of detector pairs of this invention may be constructed to measure laser beam intensity across the breadth of the beam to ascertain the intensity profile of the incident beam.