A semiconductor material includes a compositionally-graded transition layer, an intermediate later and a gallium nitride material layer. The compositionally-graded transition layer has a back surface and a top surface, and includes a gallium nitride alloy. The gallium concentration in the compositionally-graded transition layer increases from the back surface to the front surface. The intermediate layer is formed under the compositionally-graded transition layer. The gallium nitride material layer is formed over the compositionally-graded transition layer, and has a crack level of less than 0.005 μm/μm2.