An electrophotographic single-layer organic photoreceptor consisting of relatively low concentrations of phthalocyanine pigments dispersed in an insulating binder polymer, which is generally referred to as a high gamma photoreceptor, shows the induction effect. Several mechanisms have been proposed to explain this phenomenon. However it is not completely clear at this time. In this article, the photoinduced and dark discharge characteristics of the high gamma photoreceptors consisting of x-type metal-free phthalocyanine pigment and polyester polymer are found to be well described by a new theoretical model which takes into account structural trapping. We have found that good charge acceptance and high gamma characteristics depend on the presence of structural traps.