An admittance spectroscopy technique has been developed for the interfaces between organic monolayers and silicon. The present work involves the development of an effective equivalent circuit to represent the silicon/organic-monolayer system, and the development of a parameter extraction procedure, which yields the monolayer capacitance and the monolayer thickness, the flat-band voltage, the silicon doping density, the silicon surface potential. the interface trap density, the interface trap capture cross-section and the interface trap energy. This technique was applied to three types of silicon/oroanic-monolayer system. (c) 2005 Elsevier B.V. All rights reserved.