AlGaN/AlN/GaN high electron mobility transistors (HEMT) structures with AlN interfacial layer of various thicknesses are grown by metalorganic chemical vaper deposition, and their electrical properties are investigated. The HEMT sample with an AlN layer thickness of about 1.5 nm shows a highly Hall mobility of 1680 cm2/Vs with a low sheet resistance of 310 Ω, and high two-dimensional electron gas (2DEG) density of 1.2×1013 cm-2 are obtained at room temperature, indicating good electrical properties of the HEMT material. Furthermore, the results from atomic force microscopy and high resolution X-ray diffraction measurements confirm that the samples possess well surface morphology and heterostructure interface. Thence, the well heterostructure interface enhances the 2DEG density and mobility of the HEMT materials.