Abastract: The nanosized In2O3 was synthesized via the reverse microemulsion method. The hot-wire semiconductor metal oxide gas sensor was fabricated based on the In2O3. A dense layer of SiO2 on the surface of the sensitive element was formed by chemical vapor deposition of diethoxydimethylsilane (DEMS). The SiO2 functioned as molecular sieve, thereby the diffusion of reducing gases with large molecular diameter into sensing layer, except for H2, was restricted, resulting in high selectivity and response to H2. The effect of environmental humidity on the sensor response was reduced by the compensation of reference element, and the underlying reason of reduction was discussed by gas-sensing mechanism model. The sensor had high selectivity and response to H2, low ambient temperature and humidity dependence, excellent long term stability and low power consumption.