A point defect model for (Ba, Pb)TiO3positive temperature coefficient (PTC) ceramics is presented. Analysis and calculation were made of the point defect structure and its behavior in the material. The results show that the bulk electron concentration decreases with increasing Pb content. It is necessary to raise the sintering temperature to obtain higher electron concentrations. Since the transition temperature and the diffusion rate increase with Pb content, it is also necessary to raise the cooling rate to obtain the largest PTC effect. A concept for equilibrium sintering is presented.