Epitaxial GaxIn1−xAsyP1−ylayers several microns thick have been grown on (100) InP substrates by ramp cooling. Using high‐resolution double x‐ray diffractometry, the profiles obtained from such layers could be resolved into several peaks. Chemical thinning of the layers allowed these peaks to be attributed to successive sublayers having slightly different perpendicular lattice parameters, the lattice parameter within each sublayer being constant.