In situ electrochemical impedance spectroscopy was used to study the characteristics of the passive film formed potentiodynamically on copper, in slightly alkaline solution. This film has semiconducting properties. A strong eel-relation was established between the impedance and the changes in the composition and structure of the passive film. Several parameters were examined, such as: the ionic resistivity, rho (ox) of similar to 10(10) Omega cm, the dielectric constant, epsilon (ox) of similar to 105, and the concentration of charge carriers of similar to 10(20) cm(-3)