The electrical and optical properties of n‐type germanium have been studied for doping levels greater than 5×1018 cm-3. Hall coefficient and resistivity measurements show that the electron mobility μ depends upon the specific group V donor used as a dopant and, at a given carrier concentration, increases in the order μAs≪μP≪μSb. In material doped very heavily with arsenic, a large fraction of the arsenic was found to be electrically inactive. Rapid quenching of this material resulted in larger carrier concentrations and a better correlation with crystal growth parameters. Distribution coefficients were calculated from the electrical measurements on antimony‐doped crystals grown by a solvent evaporation technique. No significant ``facet effect'' was observed for these crystals. Reflectivity measurements between 2 and 24 μ were used to deduce the electron effective mass as a function of carrier concentration. In the carrier concentration range studied (up to 8×1019 cm-3), the effective mass increases only slightly and is independent of the specific dopant. The free carrier absorption is dependent on dopant. The absorption and electrical data are correlated by using elementary conduction theory.