A gas sensor is provided which includes a hollow metallic housing, a sensor device installed in the housing, and a seal disposed in the housing to hermetically isolate between the housing and the sensor device. The housing has an inner shoulder formed on an inner periphery thereof. The seal is retained on the inner shoulder. The seal is made up of a powder body and a glass body. The powder body is made of inorganic powder and mounted on the inner shoulder. The glass body is arranged on the powder body and has a varying coefficient of thermal expansion which alleviates a difference in thermal expansion between the sensor device and the housing, thereby ensuring the stability of hermetic sealing ability of the seal in high-temperature environments.