Homogeneous polycrystalline Si 1-x Ge x were grown using a Si(seed)/Ge/Si(feed) sandwich structure under the low temperature gradient less than 0.4°C/mm. It was found that the composition of the Si 1-x Ge x was controlled by the growth temperature. The homogeneous Mg 2 Si 1-x Ge x was synthesized by heat treatment of the homogeneous Si 1-x Ge x powders under Mg vapor. The Mg 2 Si 1-x Ge x sample with the relative density of 95% was synthesized by spark plasma sintering technique. The resistivity and the Seebeck coefficient of the Si, Ge, Si 1-x Ge x and Mg 2 Si 1-x Ge x samples were evaluated as a function of temperature. It indicated that Seebeck coefficients of the Si 1-x Ge x and Mg 2 Si 1-x Ge x samples were higher than those of Si and Ge. Moreover, the Seebeck coefficient of Mg 2 Si 0.7 Ge 0.3 sample was higher than that of Mg 2 Si 0.5 Ge 0.5 and Si 0.5 Ge 0.5 samples.