New donor and oxygen precipitate in CZ-silicon are studied by means of Hall measurement, IR measurement and TEM observation. Two types of defect are observed in specimens annealed at 650-750℃, that is, rod-like defects and plate-like defects. New donor generation is mainly related to the plate-like defects, which are indentified as β-cristobalite according to the H-REM results. It is suggested that the new donor originates from the ionization of dangling bonds of silicon atoms on precipitates/matrix interfaces and is controlled by the neucleation and growth of β-cristobalite precipitates.