Thin films of AlN were grown by plasma source molecular beam epitaxy system on Si(111), Si(100), Al2O3(0001) and Al2O3(1 (1) over bar 02) substrates. X-ray studies indicated that the films were highly textured on Al2O3(0001) and Al2O3(1 (1) over bar 02), and less so on Si(111) and Si(100). The thermal conductivity of these thin films was investigated by the thermal wave-mirage technique, and a high value of 25.2 W-1 m(-1) K-1 was found for the AlN film on Al2O3(1 (1) over bar 02). The physical properties were correlated to the microstructures obtained from atomic resolution transmission electron microscopy and atomic force microscopy images.