Thick (∼3 &mgr;m) films of InxGa1−xAs grown on GaAs(100) substrates, across the whole composition range, have been examined by transmission electron microscopy and double‐crystal x‐ray diffraction. The results were compared with the observed growth mode of the material determined byinsitureflection high‐energy electron diffraction in the molecular beam epitaxy growth system. The quality of the material degraded noticeably for compositions up tox∼0.5 associated with an increased density of dislocations and stacking faults. In contrast, improvements in quality asxapproached 1.0 were correlated with the introduction of an increasingly more regular array of edge dislocations.