The effect of near-by-electrode charge injection on switching of a thin film ferroelectric capacitor is theoretically analyzed. We develop a model of switching affected by charge injection through a surface dielectric layer to calculate the coercive field of the capacitor as a function of both film thickness and maximal polarization of the switching cycle. The predictions of the model are verified by electrical measurements on sol-gel derived Pb(Zr, Ti)O-3 thin films of thickness ranging from 100 to 1000 nm with Pt electrodes. The model gives a good description of the size effect on switching in the Pt/Pb(Zr, Ti)O-3/Pt system and enables an explanation for a much smaller magnitude of this effect in Bi-containing and oxide-electrode thin films. (C) 1999 American Institute of Physics. [S0003-6951(99)00409-X].