AbstractCharacteristics of ion‐selective field effect transistors (ISFETs) and ion‐selective electrodes (ISEs) with solvent polymeric membranes were compared for slope, selectivity, drift, and hysteresis. Drift and hysteresis of ISFETs were significantly inferior to those of analogous ISEs. Experiments using conventional ISEs with internal electrolyte solutions and ion‐selective liquid membranes of different kinds indicate that both primary ion and ionophore are necessary in the internal electrolyte solution and the ion‐selective membrane, respectively, to achieve small drift and small hysteresis. It is, therefore, concluded that to realize highly reliable membrane‐solid contact devices, the interface between the membrane and the solid in membrane–solid contact devices like ISFETs and coated wire electrodes (CWEs) should be electrochemica