We have investigated the strain relaxation of intentionally lattice mismatched (±0.5%) GaInP layers grown on GaAs substrates by organometallic vapor phase epitaxy. Double axis x‐ray diffraction was used to measure the relaxation in these epitaxial layers in perpendicular 〈110〉 directions as a function of thickness. For samples in tension, the difference in relaxation between [11¯0] and  increases from 10% to 48% as the layer thickness increases from 7 to 28 times the critical thickness, hc. For samples in compression this difference is 28% at 24hc while no relaxation is measured for a sample at 6hc. These results indicate that strain relaxes anisotropically and that the anisotropy is more pronounced for samples in tension than in compression. Furthermore, the major relaxation axis was found to be [11¯0] regardless of the sign of the strain. Reciprocal space maps, generated using triple axis x‐ray diffraction, showed that the amount of microtilt of the epitaxial layers was also anisotropic. This anisotropy and the direction of the maximum dislocation density which was measured by cathodoluminescence and transmission electron microscopy, changed from  in tension to [11¯0] in compression. The fact that the major relaxation axis remained stationary while the high misfit dislocation density direction rotated indicates that a substantial number of dislocations with Burgers vectors of the ‘‘wrong sense’’ for strain relief are formed in compressed epilayers. A model in which α type dislocations are more mobile than the β type misfit dislocations regardless of the sign of the strain is consistent with all of the experimental observations. © 1996 American Institute of Physics.