We report the growth and characterization of AlGaN/GaN heterostructures with AlN/GaN superlattices as the barrier layer.It is found that the surface morphology of the heterostructure is greatly improved compared with those using the conventional alloy AlGaN barrier layer.Meanwhile, electric properties of samples with high Al composition (≥40%) are superior to the conventional alloy sanples.Low sheet resistance (251 Ω/□) is obtained for our samples with 40% Al content.