Measurements of composition of multilayer semiconductor laser wafers were performed with the aid of photoluminescence spectra. Reliable depth profiling of composition is difficult in as-grown wafers, even at low temperature, because the excess-carrier diffusion length is comparable to the layer thicknesses. With adequate reduction of the diffusion length, which in our case was done with ion implantation, the origin of photoluminescence could be restricted to a narrow region close to the excited surface. Samples were prepared for profiling by an angle-etching technique, leaving a controlled angle as small as 0.01°across the wafer, which greatly simplifies profiling measurements. Results from composition profiling of a conventional five-layer GaAs-AlxGa 1-xAs DH-laser wafer with a depth resolution better than 0.1 μm are presented.