A chemical solution deposition method was used to grow thin epitaxial GaN films on C- and R-plane sapphire substrates. The films were grown by spin-coating a gallium carbodiimide based polymeric precursor onto sapphire and pyrolyzing in NH, at 900 degrees C, During heat treatment alpha-GaN formed on the R-plane of the sapphire with the following epitaxial orientation relationship: alpha-Al2O3(0 1 (1) over bar 2)\\ alpha-GaN(1 1 (2) over bar 0); alpha-Al2O3 [2 (1) over bar (1) over bar 0]\\alpha-GaN[1 (1) over bar 0 0]. A multiple coating process resulted in films fully covering the R-plane substrates. Films deposited on C-plane sapphire were not continuous and single islands were present on the substrate surface. The morphology and microstructure of the films were characterised by SEM, XRD, and conventional and analytical electron microscopy.