The influence of a SO₂ treatment on the electrical properties of SnO₂ has been studied. It is shown that some gaseous compounds induce an important maximum on the curve of the electrical conductance as a function of the temperature of SnO₂ treated with SO₂. The temperature at the maximum conductance is connected with the nature of the electrical contacts (gold or platinum) and an important part is associated with the metal-oxide interface process. The selective aspect of the electrical response can be exploited to develop a benzene detector.