Gas‐induced conductance changes were measured on palladium‐dosed single‐crystal tin oxide (SnO2) thin films having well‐characterized surface properties. Films were fabricated using two methods: reactive sputtering and chemical vapor deposition. Film orientation and crystal structure were determined by x‐ray diffraction, while surface morphology was characterized using atomic force microscopy. Conductance changes were measured continuously on film surfaces during alternating exposure and evacuation cycles to partial pressures of H2, O2, and CO in a vacuum chamber. The conductance change was found to be proportional to the square root of the initial film conductance and was interpreted in terms of gas‐induced changes in the width of a near‐surface space‐charge layer. The variation of conductance as a function of gas pressure during alternating exposure and evacuation cycles of H2and O2is consistent with a model that involves surface reactions between coadsorbates.