A gas sensor comprising: a substrate including (a) a semiconductor base plate formed with an opening portion extending therethrough in the thickness direction, (b) insulating layers (31, 32, 33, 34) formed on the semiconductor base plate and having a partition wall portion at a place corresponding to the opening portion, (c) a heating resistor formed on the partition wall portion of the insulating layers (31, 32, 33, 34) and (d) a protective layer formed on the insulating layers (31, 32, 33, 34) so as to cover the heating resistor, a gas-sensitive layer formed on the substrate and containing a metal-oxide semiconductor that varies in electrical characteristics depending upon a variation of a concentration of a particular gas component in a gas mixture to be detected, as a major constituent, a pair of detecting electrodes for detecting a variation of the electrical characteristics of the gas-sensitive layer, wherein the detecting electrodes and the gas-sensitive layer are formed on the protective layer of the substrate, and the detecting electrodes are abuttingly engaged with the protective layer, and wherein all of a surface of the detecting electrodes on the side facing the gas-sensitive layer is abuttingly engaged with the gas-sensitive layer, characterized in that the detecting electrodes are comb-shaped when viewed in plan, and an insulating adhesive layer is provided on the substrate, formed on the protective layer of the substrate, and is in contact with the gas-sensitive layer, for improving the adhesion between the substrate and the gas-sensitive layer, and the adhesive layer is formed in an area between the pair of detecting electrodes and is in contact with peripheral portions of the pair of detecting electrodes. a substrate including (a) a semiconductor base plate formed with an opening portion extending therethrough in the thickness direction, (b) insulating layers (31, 32, 33, 34) formed on the semiconductor base plate and having a partition wall portion at a place corresponding to the opening portion, (c) a heating resistor formed on the partition wall portion of the insulating layers (31, 32, 33, 34) and (d) a protective layer formed on the insulating layers (31, 32, 33, 34) so as to cover the heating resistor, (a) a semiconductor base plate formed with an opening portion extending therethrough in the thickness direction, (b) insulating layers (31, 32, 33, 34) formed on the semiconductor base plate and having a partition wall portion at a place corresponding to the opening portion, (c) a heating resistor formed on the partition wall portion of the insulating layers (31, 32, 33, 34) and (d) a protective layer formed on the insulating layers (31, 32, 33, 34) so as to cover the heating resistor, a gas-sensitive layer formed on the substrate and containing a metal-oxide semiconductor that varies in electrical characteristics depending upon a variation of a concentration of a particular gas component in a gas mixture to be detected, as a major constituent, a pair of detecting electrodes for detecting a variation of the electrical characteristics of the gas-sensitive layer, wherein the detecting electrodes and the gas-sensitive layer are formed on the protective layer of the substrate, and the detecting electrodes are abuttingly engaged with the protective layer, and wherein all of a surface of the detecting electrodes on the side facing the gas-sensitive layer is abuttingly engaged with the gas-sensitive layer, characterized in that the detecting electrodes are comb-shaped when viewed in plan, and an insulating adhesive layer is provided on the substrate, formed on the protective layer of the substrate, and is in contact with the gas-sensitive layer, for improving the adhesion between the substrate and the gas-sensitive layer, and the adhesive layer is formed in an area between the pair of detecting electrodes and is in contact with peripheral portions of the pair of detecting electrodes.