Aluminum nitride films (AlN) were grown on silicon and quartz substrates by DC reactive magnetron sputtering. They were annealed at 600 and 800 °C for 30 min in the presence of nitrogen gas. Ellipsometry, FTIR spectroscopy, optical transmission spectrum and C-V measurements were carried out to study the optical, structural and electrical properties of AlN films. It was found that annealing enhances the optical transmittance and bandgap. Annealing also results in an increase in Al-N bond density and band broadening of AlN absorption band. XRD studies revealed that the films are amorphous in nature. The refractive index of the films did not change significantly, whereas dielectric constant decreased with an increase in annealing temperature. Positive insulator charge density (Qin) increased, whereas interface electronic state density (Dit) decreased as a result of annealing. © 2004 Elsevier B.V. All rights reserved.