2.2-μm-thick crack-free GaN films were grown on patterned Si substrates. The crack-free GaN films were obtained by patterning Si substrate and optimizing the graded Al xGa 1-xN layers. With the increase of the graded Al xGa 1-xN layer thickness, the GaN crystal quality improved as judged from the X-ray diffraction data. By applying multi-Al xGa 1-xN layers on the patterned Si substrate, a 31% reduction of tensile stress for the GaN film was obtained as measured by micro-Raman. For the AlGaN/GaN high electron mobility transistor grown on 1 × 1 cm 2 larger patterns, the device exhibits maximum drain current density of 776mA/mm and maximum transconductance of 101mS/mm.