Theoretical curves of the voltage dependence of cathodoluminescence have been obtained for the case where the intensity of cathodoluminescence varies superlinearly with the net carrier generation rate. Calculations are based on numerical integration of the distribution of excess carriers assuming a Guassian approximation to the distribution of excitation with depth. The theoretical curves make possible the measurement of diffusion lengths using the method of voltage dependence of cathodoluminescence in specimens where the intensity of cathodoluminescence is not linearly proportional to the specimen current (e.g.,p‐type GaAs). Experimental results with accelerating voltages of 5–50 kV using a defocused electron beam and selected area technique indicate values of electron diffusion length inp‐type GaAs ranging from 3.2 &mgr; at low carrier concentration (6.9×1016cm−3) to 0.6 &mgr; at high carrier concentration (3.76×1019cm−3).