C axis oriented AlN films were deposited on silicon substrate by radio frequency reactive magnetron sputtering. Subsequently the films were annealed in a horizontal furnace at temperatures ranging from 400 to 800°C for 30 min in nitrogen ambient. The change in the morphological properties with annealing temperatures was investigated using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy techniques. Morphological studies revealed that the annealing increased surface roughness and grain size. In addition, Al-N bond density along with the crystallinity of the deposited films was improved with annealing. The electrical properties, namely the insulator charge density (Qin) and the interface electronic state density (Dit), were estimated by the capacitance-voltage (C-V) measurements. It was found that the Qin increased, but the Dit decreased with annealing temperature. Lower leakage current with improved resistivity and dielectric behaviour was also observed with annealing. © 2009 Institute of Materials, Minerals and Mining.