Aluminum nitride (AlN) films were deposited by reactive direct current Magnetron Sputtering (dcMS) on Si (100) substrates, with different thicknesses, in Ar-N2 gas mixture. The films were characterized by X-ray diffraction (XRD), profilometry, scanning electron microscopy and UV-Visible Ellipsometry. The effect of the thickness on the thermal conductivity of AlN films was investigated using a fast IR pyrometry device. The XRD measurements show that AlN films are texturated along (002) direction. Moreover, X-ray rocking curve measurements indicate that the crystalline quality of the AlN is improved with the increase of film thickness. Optical analyses by IR spectroscopy and UV-Visible Ellipsometry demonstrate a high optical band gap of pure AlN films with semi-transparent behaviour in the IR range (1 to 7 μm). The effective thermal conductivity of the AlN films is strongly dependent on the film thickness. An effective thermal conductivities between (80 ± 05) and (175 ± 15) W.m−1.K−1 were measured for 260 and 8000 nm thick AlN film.