This work presents a new one-step process enabling the mask-free localized functionalization by organic polymers of the conducting or semiconducting parts of composite surfaces at the micrometer and submicrometer scale. The functionalization is carried out via cathodic electrografting of suitable precursors of composite cathodes, which gives an insulating polymer film strongly grafted to selected parts of the composite electrodes and guarantees that the resolution is that of the pre-existing patter, even when the whole surface is dipped into the reaction medium. The presumed mechanism is based on a regioselective extraction of electrons from the composite surface according to its apparent local work function in solution.