Magnesium base alloys and compounds are attractive for various applications as a functional material. In particular, a series of binary system by Mg2X (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 semiconductive compounds: high vaporizing pressure and mechanical adhesion of magnesium, reaction of germanium and tin with crucibles, and, difference of melting point among elements, X. Solidstate processing via the bulk mechanical alloying enables us to directly fabricate these Mg2X semiconductive materials in high density performs. The precise control of chemical composition leads to an investigation on the dilution and enrichment of X in Mg2X. Two types of solid-state reactivity are introduced: e.g. synthesis of Mg2Si from an elemental mixture Mg – Si, which is a nucleationcontrolled process, while synthesis of Mg2Sn from Mg – Sn is a diffusion-controlled process. The thermoelectricity of these Mg2X is evaluated for discussion on the validity and effectiveness of this new PM route as a reliable tool for fabrication of thermoelectric compounds.