A neutron activation study was performed to follow the total oxygen content during the preparation sequence of mechanically alloyed Si-20 at.% Ge n-type alloys using both elemental powders and chunk starting materials. The Si-20 at. % Ge alloys were doped with 1.6 at. % GaP and 3.4.at. % P and the total oxygen concentration was measured in the starting materials, after six hours of mechanical alloying in a helium environment, after hot pressing, and after a short 1100°C soak in fused silica ampoules. The alloys containing high oxygen levels showed low carrier mobility and low thermal conductivity whereas those containing low oxygen showed high mobility and thermal conductivity. The microstructure, as observed by optical metallography and SEM, was found to differ greatly with oxygen content as the low oxygen alloys showed relatively large, well defined grains and the high oxygen alloys showed evidence of poor sintering and limited grain growth.