A method of forming a semiconductor device may include forming a contact mold layer on a substrate; forming an interconnection mold layer on the contact mold layer that includes a material having an etching selectivity with respect to the contact mold layer; forming grooves in the interconnection mold layer that extend in a first direction and expose the contact mold layer; forming holes in the contact mold layer connected to the grooves by etching a part of the contact mold layer exposed by the groove; and forming contact portions in the holes and interconnections in the groove. A diffusion coefficient of mobile atoms in the contact mold layer is greater than a diffusion coefficient of mobile atoms in a nitride.