Micro-distribution of C acceptor defect in semi-insulating gallium arsenide (SI-GaAs) wafer has been investigated by means of chemical etching, microscopic observation, transmission electron microscope, eelectron probe x-ray microanalyz er.Experimental results show that there is a corresponding relationship between the distribution of C impurity and dislocation density in a wafer. In relatively high dislocation density areas, dislocations form relatively small cells with few isolated dislocation within each cell. Here the profile of C distribution in the area of a cell is “U”-shaped. The cell diameter increases as the dislocation density decreases, and the dislocations form relatively large cells with a few isolated dislocations within each cell. The profiles of C distributio n in the area of a cell is “W”-shaped.