In a method for manufacturing a compound semiconductor, a silicon oxide film is formed on a substrate comprising silicon. Ion implantation is then performed in a region of the substrate (101), below the silicon oxide film. Heat treatment is performed to thereby form an underlayer (102) comprising monocrystalline silicon where ions have been implanted. Next, the underlayer (102) is exposed by removing the silicon oxide film. A GaN layer (105) is then formed on the underlayer (102).