Abstract: P-type semiconductor 15 and n-type semiconductor 16 are formed as thick films or spray-coated onto electrodes 13 and 14 on top of substrates 11 and 12, with films of p-type semiconductor 15 and n-type semiconductor 16 being formed in such manner that they are in mutual contact. If a gas to be detected is introduced to the contact region while a bias voltage is being applied between the two electrodes, an output will be obtained in accordance with the concentration of flammable gas components in the gas being detected. In addition, if a film is formed from a material comprising a mixture of particles of p-type semiconductor and particles of n-type semiconductor, the bias voltage can be an AC voltage.