GaN-on-diamond samples were demonstrated using a membrane-based technology. This was achieved by selective area Si substrate removal of areas up to 1 cm × 1 cm from a GaN-on-Si wafer, followed by direct growth of polycrystalline diamond using microwave plasma chemical vapour deposition on etch exposed N-polar AlN epitaxial nucleation layers. Atomic force microscopy and transmission electron microscopy were used to confirm the formation of high quality, void-free AlN/diamond interfaces. The bond between the III-nitride layers and diamond was validated by strain measurements of the GaN buffer layer. Demonstration of this technology platform is an important step forward for the creating of next generation high power electronic devices.