AbstractThis paper describes protectors and multisensors using ferrite‐magnetic semiconductor (FMS). Useful FMS devices with Curie temperature from −15° to 300°C, in which the ferromagnetic properties below are retained below the Curie temperature, can be produced.The magnetic and electrical properties of FMS depend on temperature, humility, and gas concentration and can perform a switching function. The magnetic reluctance increases with temperature and approaches a maximum at the Curie temperature, but is independent of humidity or the concentration of combustible gases. The semiconducting resistance decreases from 225 to 170 kω as the humidity changes from 50 to 90 percent The FMS's specific dielectric constant above 900 is dependent on temperature, humidity, and the concentrations of combustible gases, including acetone, methanol, and ammonia In methanol, the capacitance increases from 0.18 to 0.5 nF as the concentration rises from 0 to 850 ppm. Bidirectional switching characteristics appear at voltages above 250 V. These characteristics should have practical applications in protective and measuring instruments. An overheating/overvoltage protector with temperatwe/humidity/gas concentration sensors composed of two annular FMSs is des