Magnesium silicide has been investigated since for over 30 years because of its superior thermoelectric characteristics and lightweight. Its practical use, however, has not been realized yet, since the main component Mg is hard to be handled. Magnesium silicide bulk is almost produced by sintering with pressing such as spark plasma sintering or hot-pressing. Sintering with pressing is unsuitable for mass-production because of the small product size and the high production cost. In this work, a modified process of usual pressure-less sintering, which is useful for mass-production, was employed to produce sintered bodies of magnesium silicide. Pressing in an inert gas atmosphere successfully yielded pressure-less sintered bodies with a sufficiently small unevenness of the characteristics. The sintered bodies obtained were confirmed to have the superior thermoelectric properties, namely a Seebeck coefficient of -162 μV/K, a resistivity of 0.15 mΩm and 2.54 W/mK for n-type; +209 μV/K, 0.017 mΩm and 2.73 W/mK for p-type.