AlN thin films have been grown on Al-coated Si(100) and Si(111) substrates by using nitridation in high-purity nitrogen ambient, where the Al layer was previously deposited on Si by ultra-high vacuum (UHV) electron beam evaporation. The temperature of nitridation was found to play an important role in the formation of AlN films. XRD results showed AlN films formed by nitridation at 1000 degrees C for 30 min exhibited good crystallinity with the preferred orientation of (002) for both Si(111) and Si(100) cases. Other analysis techniques, like Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy have been used to evidence the formation and purity of the AlN films. Scanning electron microscope observations of the films revealed a closely-packed granular texture.