Magnesium base alloys and compounds are attractive for various applications as a functional material. In particular, a series of binary system by Mg 2X (X = Si, Ge, Sn and Pb) has fascinated many researchers and engineers by its thermoelectric properties and semi-conductive performance. Many barriers in its processing rejects precise investigation of these types of semi-conductive compounds: high vaporizing pressure and mechanical adhesion of magnesium, reaction of germanium and tin with crucibles, and, difference of melting point among elements, X. Solid-state processing via the bulk mechanical alloying enables us to directly fabricate these Mg2X semi-conductive materials in high density performs. The precise control of chemical composition leads to an investigation on the dilution and enrichment of X in Mg 2X. Two types of solid-state reactivity are introduced: e.g. synthesis of Mg2Si from an elemental mixture Mg - Si, which is a nucleation-controlled process, while synthesis OfMg2Sn from Mg - Sn is a diffusion-controlled process. The thermoelectricity of these Mg 2X is evaluated for discussion on the validity and effectiveness of this new PM route as a reliable tool for fabrication of thermoelectric compounds.