SnO₂ thin-film gas sensors were easily created using the ion sputtering technique. The as-deposited SnO₂ thin films consist of a tetragonal SnO₂ phase and densely packed nanosized grains with diameters of approximately 20-80 nm, which are separated by microcracks. The as-deposited SnO₂ thin film is well crystallized, with a dense columnar nanostructure grown directly onto the alumina material and the Pt electrodes. The grain size and thickness of SnO₂ thin films are easily controlled by varying the sputtering time of the ion coater. The responses of the SnO₂ thin-film sensors decrease as the SnO₂ film thickness is increased, indicating that a negative association exists between the sensor response and the SnO₂ film thickness due to gas diffusion from the surface. The SnO₂ thin-film sensor, which was created by ion sputtering for 10 min, shows an excellent sensor response (Ra/Rg where Ra is the electric resistance under air and Rg is the electric resistance under the test gas) for detecting 1 ppm H₂S at 350°C.