An energy distribution of interface states has been considered to study the electrical characteristics of an anisotype semiconductor heterojunction. Various electrical quantities such as the surface potential, current, conductance and ideality factor of the device have been studied. The cuffent-voltage and conductance-voltage characteristics are found largely sensitive to the parameters controlling the distribution profile of interface states. A new expression for the ideality factor of the device has been derived, which predicts appreciable voltage dependence due to the distributive nature of the interface states. It has been found that the experimental I-V data of p-InP/n-CdS heterojunction reported by earlier workers can be satisfactorily explained with the help of the present model if the effect of shunt resistance of the device is included in the evaluation scheme. (c) 2005 Elsevier B.V. All rights reserved.