Thin film-based micro gas sensors using undoped and Pt-doped SnO2 thin films with thicknesses of 50 and 120nm are deposited using RF sputtering on MEMS structures and their sensing characteristics to 25ppm CO, 25ppm toluene, and 1ppm HCHO gases were investigated at 300–440°C. The Pt-doped SnO2 gas sensors with the thickness of 120nm showed the selectivity to 1ppm HCHO gas at 31.5mW power consumption and to 25ppm toluene gas at 45mW. The control of gas selectivity by tuning thickness of sensing film and Pt catalyst loading was discussed. The results of this study suggest the possibility of employing thin film-based micro gas sensors for real applications with mass productivity and cost effectiveness.