The semi-conductive properties of passive films formed on copper in chromate solutions were investigated by means of capacitance measurements. The effects of the formation potential and temperature, chloride and chromate concentration n electrolyte solution, as well as measured frequency on the semi-conductive properties of passive films were studied. The results show that the passive films formed on copper display n-type semi-conductive characteristics. The slopes of the straight lines in Mott-Schottky plots decrease with moving the formation potential toward positive, increasing the chloride ion concentration, decreasing the formation temperature and the chromate solutions concentration. Moreover, the initial grain size of copper surface impacts remarkably on the semi-conductive properties. The donor density of the passive films formed on ultra-fine grained (UFG) copper is higher than that of the passive films on coarse-grained (CG) copper. (C) 2008 Elsevier B.V. All rights reserved.