The thermal stability of strained Si/Si1-xGex epilayers with x = 0.15 to 0.25 was investigated under various thermal annealing conditions. High Resolution (HR) X-ray Diffractometry (XRD) was used to determine the intrinsic strain of the heterostructure before any thermal treatment. The effect of thermal processing on strain relaxation and Ge diffusion was observed by Raman spectroscopy and Secondary Ion Mass Spectroscopy (SIMS). Strain analysis by Raman reveals no sign of Si strain relaxation for temperatures up to 1000 degreesC for 5 min. However, Ge diffusion into strained Si was detected by both Raman and SIMS. (C) 2004 Elsevier B.V. All rights reserved.