Semiconductor gas sensors based on nanocrystalline WO3 films were produced by two different methods. Advanced reactive gas evaporation was used in both cases either for a direct deposition of films (deposited films) or to produce ultra fine WO3 powder which was used for screen printing of thick films. The deposited films sintered at 480 degreesC and the screen-printed films sintered at 500 degreesC displayed a mixture of monoclinic and tetragonal phases and had a mean grain size of approximately 10 and 45 nm, respectively. We studied the influence of the sintering temperature T-s of the films on their gas sensitivity. Unique and excellent sensing properties were found upon exposure to low concentrations of H2S in air at room temperature for both deposited and screen-printed films sintered at T-s= 480 degreesC and at T-s = 500 degreesC, respectively.