The trapping range of holes and electrons in amorphous selenium layers has been measured with a voltage decay technique. Values of 1.1 to 7.8×10−8cm2/V were obtained for holes. This agreed well with values obtained by the pulse method. An electron range of 5.0 to 8.3×10−8cm2/V was measured. Quantum efficiencies for photoexcitation of holes and electrons ranged from 7.5×10−4to 1.0, depending on the wavelength of the incident light.