A method of reducing the thickness of a wafer of semiconductor for applications, where accuracy of the substrate thickness is critical to the operation of the device, or where the thermal resistance of the substrate must be reduced to a minimum. After processing of the front side of the substrate using a planar process, a slurry of water and fine grit is used to wear down the back of the wafer. The slurry is placed between a flat plate and the back of the wafer, and the wafer moved with respect to the plate in order to remove substrate material by abrasion.