Ion sensor and ion sensor manufacturing method

This ion sensor comprises a substrate and a plurality of detection units. Each of the detection units comprises an ID unit, an ICG electrode, a TG electrode, an SG electrode, an electrode pad, and an ion-sensitive film. The SG electrode is disposed between the ICG electrode and TG electrode on the main surface of the substrate. The electrode pad is electrically connected to the SG electrode and is disposed on the reverse side of the substrate from the SG electrode. The ion-sensitive film is provided on the surface of the electrode pad and has an electric potential that changes according to variation in the ion concentration of an aqueous solution in contact with the ion-sensitive film. The width of the ion-sensitive film in the direction in which the ICG electrode and TG electrode face each other is greater than the distance by which the ICG electrode and TG electrode are separated from each other.