The effect of GaN and InxGa1-xN interlayers on the strain state and defect density of GaN buffer layers is studied. The layers are grown by low pressure MOVCD on c-plane sapphire Substrates and were investigated by in situ reflectometry, AFM, photoluminescence, high-resolution X-ray diffraction, In addition, etch pit densities are determined by wet chemical etching in hot phosphoric acid. We find that InxGa1-xN interlayers slightly decrease the defect density and reduce the strain in the GaN buffer layers. (C) 2002 Elsevier Science B.V. All rights reserved.