Damaged layers of GaP crystals surface treated by reactive ion etching using PCl3 gas are evaluated by capacitance-voltage, secondary ion mass spectroscopy, and photocapacitance (PHCAP) measurements. The reduction of the carrier concentration is observed at the surface region within the depth of 60-70 nm, where Cl atoms injected with high energy are observed. PHCAP measurement reveals that density of the deep levels increases with decreasing gas pressure. The deep levels are thought to be the complexes of shallow donor impurities and intrinsic point defects.