Fabrication of sintered undoped n-type Mg2Si, initiated from pre-synthesized all-molten polycrystalline Mg2Si powder, was carried out using a Plasma Activated Sintering technique. The thermoelectric properties were evaluated from room temperature up to 861 K. The maximum dimensionless figure of merit was estimated to be 0.60 at 861 K. For output power measurements, the length and cross-sectional area of Mg2Si elements equipped with Ni electrodes were varied from 6 to 15 mm and 2x2 to 4x4 mm(2), respectively. For the 3x3x7.5 mm(3) element, the maximum output power density was 1.43 Wcm(-2) with the temperatures of the cool and hot sides being 373 K and 873 K (Delta T = 500 K), while the highest output power was 203 mW for the sample of 4x4x7.5 mm(3) at Delta T = 500 K. The results of aging tests for 11,000 h with the hot side at 873 K and the cool side at 373 K under atmospheric conditions showed that the fabricated device elements possess sufficient durability at high power-generation operating temperatures. (C) 2011 Elsevier B. V. All rights reserved.