We have grown high Ge content SiGe virtual substrates at high temperatures in a reduced pressure-chemical vapour deposition reactor. We have notably focused on the effects of growth temperature and final germanium content on the virtual substrates' structural properties (macroscopic degree of strain relaxation, surface roughness and threading dislocation densities). Increasing the growth temperature of Si0.80Ge0.20 virtual substrates leads to a severe reduction of both the field and pile-up threading dislocation densities, while keeping a relatively smooth cross-hatched surface. A growth temperature of 950 degrees C allows one to achieve a 10(5) cm(-2) (10(4) cm(-2)) field (pile-up) threading dislocations density. For a fixed growth temperature, increasing the germanium content of virtual substrates leads to an increase of the surface roughness that is more severe at 900 than at 850 degrees C. The final Ge content (between 20% and 50%) has little impact on the field threading dislocation density, whereas it does increase the pile-up threading dislocation density. Such an increase seems to be influenced by the surface roughness. (c) 2005 Elsevier B.V. All rights reserved.