This paper describes transport measurements on the magnetic semiconductors Gd 3− x v x S 4 . The vacancies, v, are randomly distributed throughout the lattice and lead to fluctuating repulsive potentials and band tailings. Furthermore, since our largest measured carrier concentrations are small compared to the maximum number of vacancies ( ∼2.3×10 21 cm −3 ), a rigid band model should be applicable. This is in contrast to ordinary semiconductors where the energy dependence of the density of states is generally a strong function of the dopant concentration. Recent transport measurements in Eu doped EuS, which demonstrate the applicability of a model for transport in a band tail of localized states will also be reviewed. The two systems will be compared and discussed in terms of a model first suggested by Cutler and Mott for paramagnetic Ce 3− x v x S 4 , and modified here to include magnetic interactions.