The effect of a thin AlN layer inserted between AlxGa1-xN/GaN heterostructures grown on sapphire substrates was investigated for possible application in power electronic devices. The heterostructures with two different Al compositions (0.35 and 0.49) were applied to study. After growing a thin AlN (~21nm) on the buffer GaN/sapphire substrate, then a thick AlxGa1-xN/GaN heterostructure were grown and investigated the Al mole fractions. Low rocking curves were also achieved with 0.35 and 0.48 for the 0.3 and 0.49 Al compositions, respectively. The experimental results show that with an increasing of Al composition, the crystallinity is also improved with lower surface roughness. The AlxGa1-xN/GaN heterostructures with 0.35 and 0.49 Al compositions were also investigated the electrical characteristics to confirm that they are suitable for development in optoelectronic and power electronic devices such as HEMTs, LED, etc.