A model of ferroelectric switching in thin films which also exhibit semiconducting properties is presented. The two principle assumptions upon which the model is based are (1) that the threshold field for reverse domain nucleation,Ecm, is much greater than the field required for domain wall motion,Ecm, and (2) that the electrode-film interface is modeled as a metal-semiconductor interface. A film thickness dependence of the coercive field is qualitatively predicted by the model. When applied to the experimentally determined thickness dependence of coercive field in lead-zirconate-titanate thin films, the model predicts a donor concentration,ND, of 1018cm−3and a space charge surface layer thickness,W, of 0.2 μm.