Abstract: Hydrogen ion (H+) is injected into a Si (111) substrate (base substrate) 10 at the approximately ambient temperature at a doping rate of 1×1016/cm2 and at an accelerating voltage of 10 keV. As a result, an ion injection layer whose ion concentration is locally high is formed at the depth h≈100 nm from the surface (ion injection plane) by injecting ion. About 300 nm of AlGaN buffer layer 20 is formed on the ion injection front of the Si substrate 10, and about 200 &mgr;m of gallium nitride (GaN) layer 30 is deposited thereon as an objective semiconductor crystal. In this crystal growing process, the Si substrate 10 is ruptured at the ion injection layer and is finally separated into about 100 nm of thin film part 11 and a main part of the Si substrate 10. According to this method for producing a semiconductor crystal, a single crystalline gallium nitride (GaN) which has more excellent crystallinity and less cracks than a conventional one can be obtained.