The creation of defects in GaP bombarded with MeV 4He ions has been studied under ultra-high-vacuum condition by Rutherford backscattering/channeling (RBS/C) method. Our experimental results suggest that the defect generation rate is strongly related to the surface condition. When the GaP is covered with a thin amorphous layer, a significant ion beam annealing effect will be observed. The present results show that for GaP the damage is produced mainly by nuclear collision.