High-resolution X-ray diffraction was used to study the structural properties of InGaAs/AlAs/AlAsSb coupled double quantum wells (CDQWs) grown on an InP (0 0 1) substrate by molecular beam epitaxy. The InGaAs composition and the AlAs layer thickness were the considered parameters. High-resolution rocking curve measurements and two-dimensional reciprocal space mapping (RSM) were employed in both symmetrical and asymmetrical reflections. All samples showed extended satellite peaks in the rocking curves, although the sample with largest residual strain (03125) had broader satellite peaks. Symmetric RSMs indicated that none of the samples had a crystallographic tilt between the quantum well (QW) layers and the substrate. A clear strain gradient in the CDQW layers was observed in the RSM of the sample 03125, which was caused by a large residual strain. (C) 2008 Published by Elsevier B.V.