A pH sensor comprises: a chamber for receiving an electrolyte solution; a first and a second ion-sensitive field effect transistor (ISFETs), each of the first and second ISFETs having a source terminal, a drain terminal and a transistor channel extending between the source terminal and the drain terminal, a dielectric layer with a sensing surface arranged in the chamber so as to be contactable by the electrolyte solution, the dielectric layer separating the sensing surface from the transistor channel; a first measurement circuit configured to measure a first source-drain resistance across the transistor channel of the first ISFET; and a second measurement circuit configured to measure a second source-drain resistance across the transistor channel of the second ISFET. The first and second measurement circuits include a common reference electrode, the reference electrode arranged contactable by the electrolyte solution in the chamber. The dielectric layer of first ISFET has a first thickness and the dielectric layer of the second ISFET has a second thickness different from the first thickness.