In this paper, the electrical and gas-sensing properties of calcined tungsten trioxide semiconductor materials were investigated. X-ray diffraction, scan electron microscopy and infrared were used to characterize structure and performance of WO3 semiconductor material. The average grain size of WO3 was 22 nm after calcination at less than 800 degreesC and 24-26 nm at more than 900 degreesC for 1 h. The sensors of indirect heating type were fabricated. The effects of calcining temperature and operating temperature on electrical resistance and sensitivity, and sensitivity-gas concentration properties of the WO3-based sensors were investigated. The sensor based on WO3 exhibited high sensitivity and good response characteristics to ethanol gas. The electrical properties of WO3 were analyzed and the sensitive mechanism was discussed.