An effective way to improve sensor selectivity and stability is the use of catalytic filters to block interfering and poisoning gas molecules from reaching the sensor surface. Mesoporous silica with high resistivity and hugh surface areas are ideally suited as a base material for this application. When impregnated with proper catalysts, mesoporous silica has a great potential to eliminate responses to undesired gases even of thin-film and/or micro-machined sensors. In this paper, we report our initial results on thick film SnO2-based gas sensors covered with a catalytic filter consisting of Pd and Pt loaded mesoporous silica. Results indicate that selective oxidation of CO in the catalytic filter leads to the elimination of CO interference to a CH, sensor with no perceptible deterioration in sensing performance. (C) 2003 Elsevier Science B.V. All rights reserved.