Abstract: A production method for a semiconductor substrate for producing a high quality SGOI substrate 10 in which the dislocation density in a silicon germanium Si1-yGey layer (SGOI layer) formed on an embedded oxide film is reduced and the occurrence of defects is suppressed, by employing the SIMOX method, or a semiconductor substrate. The SGOI substrate is produced by adjusting the composition ratio (x) of the germanium Ge in the silicon germanium Si1-xGex layer prior to the SIMOX method processing, to a composition ratio of a predetermined ratio or less in which the dislocation density in the silicon germanium Si1-yGey layer after the SIMOX method processing becomes a predetermined level or less. Preferably the composition ratio (x) is adjusted to a composition ratio in which the dislocation density in the silicon germanium Si1-yGey layer (SGOI layer) after the SIMOX method processing becomes 106 cm?2 or less.