A new non-destructive measurement method for characterization of Si(1-x)Ge(x) based multi-layer structures, including SiGe epitaxial layer and the adjacent strained Si epitaxial layer, has been developed. The method is based on a small signal surface photo-voltage technique and allows measurement of germanium concentration and thickness of top epitaxial layer. A new physical model and a measurement algorithm were developed. The results of the measurement of a set of SiGe samples with various germanium concentration and silicon layer thickness values are presented. The characteristic mixed crystal parameter-the coefficient representing the energy gap dependence on Ge content was calculated. (C) 2008 Elsevier B.V. All rights reserved.