The authors report the growth of crack-free GaN on Si(1 1 1) substrate with step-graded AlGaN intermediate layers all grown at 1120 degrees C. By preparing all these layers at high-temperature, we can simplify the growth proceduce and minimize the growth time. Using X-ray diffraction and transmission electron microscopy, it was found that the high-temperature step-graded AlGaN intermediate layers can effectively reduce the tensile stress on GaN epitaxial layers. Photoluminescence and Raman measurements also indicate that we can improve the crystal quality of GaN by inserting the step-graded AlGaN intermediate layers. (C) 2010 Elsevier B. V. All rights reserved.