A method to study microhomogeneity of deep centres in high resistivity and low resistivity semiconductors is described herein. It uses measurements of current decay induced in Schottky diodes and p-n junctions by a probing electron beam of an SEM and is closely related to a method of photoelectron relaxation spectroscopy. The advantages of this method are demonstrated for an example of dislocation-related inhomogeneity in semi-insulating GaAs.