A lateral trench in a semiconductor substrate is formed by the following steps. Form a lateral implant mask (LIM) over a top surface of the semiconductor substrate. Implant a heavy dopant concentration into the substrate through the LIM to form a lateral implant region (LIR) in the substrate. Strip the LIM exposing the top surface of the substrate. Form an epitaxial silicon layer over the top surface of the substrate burying the LIR. Form a trench mask over the epitaxial layer. Etch a trench reaching through the epitaxial layer and the LIR. Form oxidized trench sidewalls, an oxidized trench bottom and oxidized sidewalls of the LIR. Etch the oxidized sidewalls of the LIR until the LIR is exposed. Form laterally extending trenches by etching away the LIR.