We report an x‐ray diffraction study of partially relaxed In(0.20)Ga(0.80)As layers grown simultaneously on (100) GaAs substrates and misoriented GaAs substrates. We have measured the magnitude and direction of the tilt between (100) InGaAs and GaAs planes, as well as the relaxation coefficients in 〈011〉 directions. Our results show that in many respects, the misorientation of the substrates strongly influences the relaxation of the mismatch strain. The magnitude of the tilt is always larger on misoriented substrates and approximately twice the value measured on flat substrates. The direction of the tilt changes with increasing thickness and the two directions are always 135° apart from one type of substrate to the other. In addition, for thin layers, the residual strain is about five times larger on misoriented substrates but becomes comparable for both orientations, when the layers relax further.