A seed layer as a laminate of a GaN layer (second seed layer) and an AlN buffer layer (first seed layer) is formed on a sapphire substrate. A front surface thereof is etched in the form of stripes with a stripe width (seed width) of about 5 m, a wing width of about 15 m and a depth of about 0.5 m. As a result, mesa portions each shaped like nearly a rectangle in sectional view are formed. Non-etched portions each having the seed multilayer as its flat top portion are arranged at arrangement intervals of L20 m. Part of the sapphire substrate is exposed in trough portions of wings. The ratio S/W of the seed width to the wing width is preferably selected to be in a range of from about to about . Then, a semiconductor crystal A is grown to obtain a thickness of not smaller than 50 m. The semiconductor crystal is separated from the starting substrate to thereby obtain a high-quality single crystal independent of the starting substrate. When a halide vapor phase epitaxy method is used in the condition that the V/III ratio is selected to be in a range of from 30 to 80, both inclusively, a semiconductor crystal free from cracks can be obtained.