GdSi crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Gd is bonded in a 7-coordinate geometry to seven equivalent Si atoms. There are a spread of Gd–Si bond distances ranging from 2.99–3.18 Å. Si is bonded in a 9-coordinate geometry to seven equivalent Gd and two equivalent Si atoms. Both Si–Si bond lengths are 2.49 Å.