In this report, both normal and lateral lattice parameters of partially-relaxed (110) surface Silicon-Germanium-on-Insulator (SGOI) layers are precisely determined by using asymmetric reflection XRD measurements. Moreover, relaxation rates of these SiGe layers are evaluated by using the values obtained from the XRD measurements. It is found, as a result, that anisotropic lattice relaxation between [-110] and [001] directions occurs in the (110) SGOI layers and that it is much harder to relax the lattices along [-110] direction than along [001] direction. This anisotropic lattice relaxation is attributable to the generation of twins on (111) glide planes. (c) 2008 Elsevier B.V. All rights reserved.