Metal-semiconductor schottky diode type gas sensors for enhancing gas selectivity were prepared by ion coating of gold on sintered SnO₂ pellets which were impregnated by Pd, Pt and Co. Their gas sensitivities and selectivites, gas detection methods and their I-V characteristics were investi-gated with the variation of sensing temperatures, gas concentrations and the kinds of gas. The gas sensitivity was improved by Pd and Pt, especially for Pd impregnated sensor element its sensitivity to H₂ was confirmed at room temperature. Also the gas selctivity could be improved by setting the sensing temperature at optimum value. The potentiostatic method was better than the galvanostatic method in the regeneration aspect of a sensor element. From the I-V characteristics of diode type gas sensor, H₂ concentration was measured at room temperature by detecting the current under low bias potential and the gas sensitivity to hydrogen was higher in the presence of Pd than Pt.