Catalytic metal insulator silicon carbide field effect devices, MISiCFET, have been developed as gas sensitive devices. They functioned in a corrosive atmosphere of hydrogen / oxygen alternating pulses up to 775 degreesC. At 600 degreesC some devices operated with full gas response to hydrogen for 17 hours. Below a temperature of 500 degreesC the gas response of the devices was very stable with no base line drift for several days. MISiC Schottky diodes have been used for cylinder specific monitoring of an engine and exhausts and flue gas diagnosis. The MISiCFET devices will increase the number of possible applications for FET gas sensor devices.