Magnesium-silicon thin films are deposited on glass substrates by ion beam sputtering in employing the target composed of Mg and Si plates. Thin films consist of magnesium silicide (Mg₂Si) intermetallics in the case of the target where the area ratio of Mg to Si is 50%:50%. Structural, mechanical, and electrical properties of the thin films are evaluated. The films show two-layers structures; the upper one consists of the crystalline Mg₂Si with columnar structures and the lower shows amorphous structures. The elastic modulus and hardness of the amorphous layer are higher than those of the crystalline. The film indicates semiconducting properties where the resistivity decreases with increasing temperature. In this paper, the behavior in forming Mg₂Si thin films, in particular Mg migration to surface and its evaporation from the film surface, is discussed in terms.