Tin dioxide (SnO₂) is sensitized for different gaseous compounds by heating at 500°C in an SO₂--air mixtures. Such treatment induces strong modifications of the electrical properties of SnO₂ and constitutes an attempt to solve the problem of selectivity for chemical sensors. According to the nature of the surrounding gas, the electrical conductance curves as a function of the temperature present a maximum at different temperatures: 400 °C with C₆H₆ and 100°C with H₂S. These maxima, whose values are related to the gas concentration, can be used for selective gas detection. A benzene detector device using two sensors heated to 400 and 500°C respectively selectivity for a large number of gaseous compounds.