Transport properties of (Ga, In)P are reported to 6 GPa pressure. Room-temperature Hall and resistivity measurements show a transition in mobility from Ito X-band conduction and a corresponding maximum in the Hall constant at 2.8 GPa. Room-temperature photoluminescence was measured to determine the increase in the I -band gap with pressure at a rate of 0.096+0.005 eV/GPa. A two-band model was used to explain the transport measurements.