By inserting low temperature AlN, a thicker GaN layer on Si substrate without crack was obtained. After comparing the pit densities, etching pit densities, and calculating the dislocations from XRD measurements, results indicated that adding more insertion layers further improved the crystalline quality. The electrical properties were studied by the fabrication of HEMT. The results showed that the off-state drain leakage current was reduced by about two orders magnitude from 1.6 x 10(-1) mA/mm to 3.2 x 10(-3) mA/mm. Moreover, I-Ds,I-max and g(m,max) could be optimally increased. (C) 2015 Elsevier B.V. All rights reserved.