A monitor for high‐energy beams of charged particles utilizing the phenomenon of secondary emission is described. The primary beam to be monitored passes through a set of foils alternately phased in voltage. The current produced by secondary electrons ejected by the beam passage is collected onto the one set of foils and measured. Results of tests with high‐energy electrons are given. The monitor gives no indication of saturation up to peak current densities of 16 ma/cm2, and is independent of the primary beam energy in the range over which the monitor was tested (111–235 Mev).