Ga1-xInxP layers are grown on GaAs/Ge substrates by metalorganic vapor phase epitaxy and studied by means of synchrotron X-ray topography and high-resolution X-ray diffractometry. Misfit dislocations (MDs) in Ga0.5094In0.4906P epilayers having a + 3.8 x 10(-4) lattice mismatch to GaAs/Ge substrates at room temperature (RT) are observed. Ga0.4995In0.5005P epilayers having a lattice mismatch of -3.5 x 10(-4) to the GaAs/Ge substrates at RT are shown to be free of MDs, which is explained by the different linear thermal expansion coefficient of the epilayer from that of the substrate material compensating the lattice mismatch at the growth temperature of 610 degrees C. The Matthews-Blakeslee model for critical thickness was matched to the observed MID pattern in the samples. Additionally, faceted InP hillocks and strain fields beneath them are observed within the GaInP layers. The observed MDs, which are most likely of the 60 degrees mixed < 101 > {111} type, originate at the hillocks. (C) 2009 Elsevier B.V. All rights reserved.