In the paper synthesis of magnesium silicide (Mg2Si) features on silicon crystal with different aspect ratio were observed. These crystals were etched from monocrystalline borondoped silicon wafers with (100) orientation by metal-assisted chemical etching. The synthesis was occurred in ultra-high vacuum condition by a solid phase epitaxy and the modified reactive epitaxy with ultrafast Mg deposition. The substrate temperature range in both methods was  340–390 °C. As result co-axial core-shell Si/Mg2Si heterostructures with magnesium silicide thickness 500–1200 nm were produced.