Processes for forming full graphene wafers on silicon or silicon-on-insulator substrates. The processes comprise formation of a metal carbide layer on the substrate and annealing of the metal carbide layer under high vacuum. For volatile metals, this annealing step results in volatilization of the metal species of the metal carbide layer and reformation of the carbon atoms into the desired graphene wafer. Alternatively, for non-volatile metals, the annealing step results in migration of the metal in the metal carbide layer to the top surface of the layer, thereby forming a metal rich top layer. The desired graphene layer is formed by the carbon atoms left at the interface with the metal rich top layer. The thickness of the graphene layer is controlled by the thickness of the metal carbide layer and by solid phase reactions.