Electrophotographic development characteristics of thin-film CdS photoconductors over a wide thickness range (0.17 to 1.6 mu m) are experimentally investigated. It is observed that the deposited amount of pigment measured as a function of the surface voltage of the CdS photoconductor is not dependent on its thickness. The observation proves that the surface voltage rather than the surface charge density explicitly determines the printed pigment density. Pigment adhesion force measurements have revealed that there is no significant interaction between the CdS surface charge and the toner charge. Therefore, it is concluded that the surface charge density on thin-layer photoconductors is only indirectly involved in the uniform area development process.