Data are presented on the planar (top–down) oxidation of gradedAlxGa1−xAsupper confining layers of quantum well heterostructures in order to realize high resolution square-edge lasers (or waveguides). A model is developed to facilitate composition grading ofAlxGa1−xAsfor vertical-wall (square corner or edge) planar oxidation at convenient oxidation times and tolerances. A simple AlGaAs–GaAs quantum well laser structure is used to demonstrate the square-wall (square-corner) planar oxidation method. ©1997 American Institute of Physics.