Self-assembly of amine-terminated layers on a transistor gate dielectric leads to gating of the transistor even without the use of a reference electrode or any voltage drop across the organic layer. This effect was studied using in situ electrical measurements, Kelvin probe force microscopy and X-ray photoelectron spectroscopy of (3-aminopropyl)-trimethoxysilane (APTMS) gated transistors. Current-voltage characteristics measured during the self-assembly process showed that the gating occurs only following exposure of the device to ambient humidity. X-ray photoelectron spectroscopy measurements of the layers showed a high percentage of protonated amine groups on the surface. Therefore, it is concluded that the charging of the amine group due to protonation under ambient conditions is the cause for the molecular-gating. (C) 2011 Elsevier B. V. All rights reserved.