A gas sensor using an ionic conductor has a thin-film gas detection portion on an alumina substrate. The gas detection portion comprises a zirconia ionic conductor layer, a pair of platinum electrodes provided with the ionic conductor layer interposed therebetween, and a pair of junction layers positioned between the ionic conductor layer and each electrode and formed in a state in which the substances of the ionic conductor layers and the electrodes are mixed therein.The gas sensor using an ionic conductor is formed by sequentially forming a first electrode, a first junction layer, an ionic conductor layer, a second junction layer, and a second electrode by a physical vapor deposition method on a substrate, wherein the first and second junction layers are formed to be in a state in which the substances of the ionic conductor layers and the electrodes are both present.