Selectivity to a specific gas can be achieved by depositing catalytic filter layer over the SnO2 sensing element. Two kinds of filter materials are used: intrinsic Nb2O5 and n-type semiconducting SnO2 doped with Pt. Using a filter layer, hydrocarbon sensor and alcohol sensor with excellent selectivity were made. Pt doped SnO2 filter for hydrocarbon sensor gives negligible response to the interfering gases such as ethylalcohol and cigarette smoke. On the other hand, Nb2O5 filter exhibits small interference to breath and propane gas for the detection of alcohol gas. (C) 2002 Published by Elsevier Science B.V.