From the capacitance–voltage dependence of Pt/PbZr0.5Ti0.5O3/Pt capacitors, we mathematically separated the capacitance into two parts corresponding to two regions of the samples, the uniform electric-field region and the nonuniform region. They are correlated with the bulk ferroelectric film region and the Pt/PbZr0.5Ti0.5O3 Schottky barrier interface region, respectively. The calculations based on the in-series capacitor model show a slight decrease of dielectric permitivity for the fatigued bulk films. By assuming a much smaller dielectric permitivity of the interface region than that of bulk films, it was found that the interface capacitance decreased remarkably compared with that of the bulk ferroelectric film after fatigue. This decrease was attributed to the lowering of ferroelectricity in the interface layer, which suggests that the fatigue is mainly an interface state controlled process. The asymmetricity in the interface capacitance–voltage curve is attributed to the different defect concentration levels in the top and bottom interface regions. © 2001 American Institute of Physics.