The variations of the electrical response of SnO₂ thick film sensors (10-80 µm) prepared by screen-printing technology versus their thickness depend on the studied gases: at 500 ◦C, the ratio Ggas/Gair for CO (300 ppm) presents a maximum while the ratio for ethanol (100 ppm) continuously decreases with increasing thickness. A simplified geometrical model based on a resistivity distribution within SnO₂ depleted area, depending on oxygen consumption by the reducing gas, is presented. This model takes into account the role of the metal (gold electrodes) which enhances the creation of space charge area thanks to the three boundary points "gas-metal-oxide". Calculation of conductance (G) using the proposed model allows to simulate the influence of the thickness on the response for both studied gases.