In this paper, we demonstrate the use of a monolayer film electrografted via diazonium chemistry for controlling the potential response of a field-effect transistor (FET)-based sensor. 4-Nitro-benzenediazonium salt is electrografted on an extended-Au-gate FET (EG-Au-FET) with or without using a radical scavenger by cyclic voltammetry (CV), resulting in the formation of a monolayer or multilayer. In particular, the surface coverage of the aryl-derivative monolayer on the Au gate electrode gradually increases with increasing number of potential cycles in CV. Here, Au exhibits a strong catalytic action, resulting in the oxidation of organic compounds. Uric acid is used as a low-molecular-weight biomolecule for interference. The denser the surface coverage of the grafted monolayer, the smaller the potential response of the EG-Au-FET because the redox reaction of uric acid with the Au gate surface is suppressed. On the other hand, the effect of the aryl-derivative multilayer on the suppression of the potential response was smaller than that of the monolayer because the electrogenerated aryl radicals did not react with the Au surface but with the grafted species, resulting in an exposed part of the Au surface among the grafted aryl molecules. Thus, a platform based on such a monolayer film electrografted via diazonium chemistry is suitable for controlling the potential response based on the interference of low-molecular-weight biomolecules in biosamples.