The theory for transient space-charge-limited currents in photoconductor-dielectric structures is presented. The analysis gives the transient current density and voltage across the photoconductor as a function of time for various values of. Here is a parameter that characterizes the photoconductor-dielectric structure and depends upon the relative thicknesses and dielectric constants of the two regions. In two limiting cases, our results reduce to the direct-contact (no dielectric) and open-circuit (dielectric of infinite thickness) configurations already discussed in the literature. Our rigorous mathematical expressions, involving integrals of the exponential integral, differ somewhat from the original work on the direct-contact case, although numerical results are essentially the same. The general theory presented here will broaden the spectrum of techniques already available for determining drift mobilities in insulating solids, and the relative merits of various photoconductor-dielectric geometries are discussed. © 1970 The American Physical Society.