A gas sensor includes: a first conductive layer; a second conductive layer including a first region having a first thickness and a second region having a second thickness larger than the first thickness; a metal oxide layer disposed between the first conductive layer and the second conductive layer, the metal oxide layer including a bulk region and a local region surrounded by the bulk region, a degree of oxygen deficiency of the local region being higher than that of the bulk region; and an insulation layer covering the first conductive layer, the second region of the second conductive layer, and the metal oxide layer and not covering the first region of the second conductive layer.