The RSM711 is a metal oxide semiconductor type sensor in which a sensor layer and a heater layer are formed on an alumina substrate. It can detect the gaseous air contaminants. In the sensor, the sensing materials are placed on the alumina substrate, and the resistance of the sensing material is varied according to the concentration of the air pollution gases. The RSM711 is fabricated on the TO-5 package with several holes. It can reduce the influence of interference gases as well as protect from humidity or dust.