Affords a III-V compound semiconductor substrate manufacturing method that enables enhancement of the substrate PL intensity. In such a III-V compound semiconductor substrate manufacturing method, first, the surface 3a of a wafer 3 is polished (polishing step). Second, the surface 3a of the wafer 3 is cleaned (first cleaning step S7). Next, the surface 3a of the wafer 3 is subjected to first dry-etching, employing a halogen-containing gas, while first bias voltage is applied to a chuck 24 for carrying the wafer 3. Subsequently, the surface 3a of the wafer 3 is subjected to second dry-etching, employing the halogen-containing gas (second dry-etching step S11), while second bias power lower than the first bias power is applied to the chuck 24.