A gas sensor for detecting the concentration of a detection target gas in an atmosphere of interest is disposed on an electrically insulating member. The gas sensor includes an insulating porous layer formed of an electrically insulating porous material, a reference electrode, a solid electrolyte body, a detection electrode that are stacked in this order on the electrically insulating member, and a reference electrode lead disposed between the insulating member and the insulating porous layer. The insulating porous layer defines a through hole in a region sandwiched between the reference electrode lead and the reference electrode. An electrically conductive member formed of a material having electrical conductivity is disposed in the through hole so as to extend from an opening of the through hole at one end thereof to an opening of the through hole at the other end thereof.