Indium doping of nominally puren‐type CdS containing excess Cd can raise the free‐carrier concentration by an order of magnitude over the 77–300 °K temperature range even though this increase is only a small fraction of the total concentration of indium impurities included as dopants. At room temperature such doping does not significantly change the mobility from its value in undoped samples. As temperature is lowered toward 77 °K, neutral‐impurity‐like scattering in the indium‐doped samples causes the mobility to become only weakly dependent on temperature. This is in contrast to undopedn‐CdS which is dominated by longitudinal polar optical‐phonon scattering and piezoelectric scattering that allow the mobility to rise an order of magnitude as temperature is lowered from 300 to 77 °K.