Irradiation of dielectrics with nonpenetrating electron beams generates long‐lasting space charges. A simple experimental and mathematical method is developed for the investigation of charge buildupduringirradiation. Time‐resolved charge measurements carried out with pulsed beams of 1‐MeV electrons, pulse duration of 4×10−5sec, and an average current density of 10−2A/cm2were used to analyze effects of charge leakage caused by radiation‐induced conductivity and electron range reduction caused by retardation of the incident electrons in the internal space‐charge field. Leakage is found to predominate in silica and borosilicate glass while range reduction predominates in polyethylene.