High–pressure phase stability of gallium phosphide was explored under different hydrostatic environments up to 40.0 GPa in a diamond anvil cell. Two irreversible phase transitions from the semiconductor to metal to an amorphous state appear at 19.8 and 31.5 GPa and as well as 22.6 and 35.3 GPa under nonhydrostatic and hydrostatic environments, respectively. Furthermore, the hysteresis effect of the high–pressure phase transition of a sphalerite–structure compound under a hydrostatic environment was disclosed. All of the obtained results can provide new insight into the underlying structural evolution and electrical transport characteristics for the semiconducting compound at different hydrostatic environments.