When the thickness of InGaN film grown on (0 0 0 1) GaN is beyond a critical value, the compressive strain will be relaxed through dislocation generation or three-dimensional growth. We calculate the InGaN critical thicknesses for dislocation generation and three-dimensional growth depending on the indium composition, respectively. The results show that both the critical thicknesses decrease with increase of the indium composition. When the indium composition is lower than 27%, the latter is smaller. This means three-dimensional growth will be induced more easily than the dislocation generation. But when the indium composition is higher than 27%, dislocations become to generate more easily. The extension of dislocations from GaN into InGaN can relax a part of strain and increases the critical thickness. (C) 2011 Elsevier B.V. All rights reserved.