We present results obtained with microstructured tin dioxide-based gas sensors. Thick films with controlled nanocrystallite sizes were deposited on micromachined substrates. Discrimination between CO, CH 4 , and C 2 H 5 OH, and between CO, CH 4 and H 2 in changing humidity conditions was achieved by simultaneously measuring temperature and resistance changes upon gas exposure. These results make it possible to fulfil the American and European safety standards for CO and CH 4 detection with tin dioxide based gas sensors. The physico-chemical origin of temperature and resistance changes are discussed.