The effects of SiO2 coating on gas-sensing properties of SnO2 thin film sensors with interior electrodes have been investigated. The thicker the SiO2 film, the higher the H-2 sensitivity of the SnO2 film in the double-layer SiO2/SnO2 structure. Significant enhancement in H-2 sensitivity was also achieved with the SiO2 coating films having a large volume fraction of small pores. The SiO2 coatings also induced a drastic slowdown of recovery speed after removal of H-2. From these results, restricted O2 permeation into the interior SnO2 film, in comparison to H-2 diffusivity, is suggested to be responsible for the significant enhancement in H-2 sensitivity. Under the same conditions, however, enhancement in CH4 sensitivity was relatively small. Thus, it was revealed that H-2 sensing properties of SnO2 sensors with interior electrodes can be modified by controlling the gas diffusion process.