Drift mobility measurements have been made on thin amorphous films of selenium-sulfur alloys in the composition range from 14 at % to 31 at % sulfur. Carrier lifetimes were found to be 10-20 μsec for holes and > 10-3 sec for electrons. These lifetimes are considerably longer than those reported by Schottmiller et al. in lower sulfur concentration films. The drift mobilities decrease with increasing sulfur concentrations and were characterized by activation energies of 0.33 eV for holes and 0.43 eV for electrons. Only a trap-controlled drift mobility model is consistent with the constant activation energies and decreasing mobility observed with increasing sulfur content. The optical absorption and photoconductivity edges were found to shift to higher photon energies with increasing sulfur content. © 1973.