A semiconductor die is disclosed comprising a lateral semiconductor device on an upper major surface of a substrate, the integrated circuit comprising a silicon layer over the substrate, a recess in the silicon layer, a layer of LOCOS silicon oxide within the recess and having a grown upper surface which is coplanar with the surface of an un-recessed portion of the silicon layer, wherein the silicon layer beneath the recess has a non-uniform lateral doping profile, and is comprised in a drift region of the lateral semiconductor device. A method of making such a die is also disclosed, as is an integrated circuit and a driver circuit.