The H2S sensing characteristics of SnO2 thin films loaded with CuO were found to be much improved by reducing the film thickness. A 40-nm-thick film showed sensitivity as high as 20000 and 2000 to 1.5 and 0.3 ppm H2S in air, respectively, at 200 degrees C, while the rate of response to 0.3 ppm H2S was rather slow.