Fine rod and whisker‐type crystals of undoped CdS whose dark conductivity was of the order of 10−10(&OHgr;‐cm)−1were bombarded with 100‐keV electrons. Following bombardment dark conductivity of the order of 10−3(&OHgr;‐cm)−1was observed. Heat treatment to about 200°C reduced the conductivity to near its original value. Because of the high efficiency with which the electron beam raised the conductivity of the crystals, an explanation based on the redistribution of electrons and holes over existing levels rather than the production or removal of defects is required.