Abstract: Disclosed is a sensor comprising an insulating substrate, a plurality of electrodes coated on the insulating substrate and formed of a thin film conductor of a metallo-organic compound obtained by a pyrolysis, and a layer formed across the electrodes. The layer formed across the electodes has an electrical property changeable in accordance with an atmosphere. The sensor reduces the affection due to the existence of the step portion, restrains the structural deficiency at the step portion and improves the stability of the change with age. By the metallo-organic compound, the thin film layer can be formed by a pyrolysis at relatively low temperatures, and the electrodes can be formed in various structures and by various producing processes.