Fabrication of Mg2Si1-xGex (x=0-1.0) was carried out using a spark plasma sintering technique initiated from melt-grown polycrystalline Mg2Si1-xGex powder. The thermoelectric properties were evaluated from RT to 873 K. The power factor of Mg2Si1-xGex with higher Ge content (x=0.6-1.0) tends to decrease at higher temperatures, and the maximum value of about 2.2 x 10(-5) Wcm(-1) K-2 was observed at 420 K for Mg2Si and Mg2Si0.6Ge0.4. The coexistence of Si and Ge gave rise to a decrease in the thermal conductivity in the Mg2Si1-xGex. The values close to 0.02 Wcm(-1) K-1 were obtained for (MgSi1-xGex)-Si-2, (x=0.4-0.6) over the temperature range from 573 to 773 K, with the minimum value being about 0.018 Wcm(-1) K-1 at 773 K for Mg2Si0.4Ge0.6. The maximum dimensionless figure of merit was estimated to be 0.67 at 750 K for samples of Mg2Si0.6Ge0.4. (c) 2007 Elsevier B.V. All rights reserved.