The effect of Cu addition on the electrochemical corrosion behavior of austenitic, ferritic and martensitic stainless steels in both the active and passive state was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in 0.1 M H2SO4. The semiconducting properties of the passive films were investigated by capacitance measurements by using the Mott-Schottky approach. Cu addition generally improved corrosion resistance and facilitated passivation but did not notably affect the resistance of the passive films. Capacitance results revealed that the passive films behave as n-type and p-type semiconductors at potentials below and above the flatband potential, respectively. Cu addition caused an increase in the donor and acceptor densities, which we have attempted to correlate with the passive film stability. (C) 2010 Elsevier Ltd. All rights reserved.