Current leakage sites in diamond p–n junction are determined by measuring an electron‐beam–induced current (EBIC) technique and conductive atomic force microscopy (C‐AFM). Current leakage sites in p–n diodes, particularly, can be determined by means of EBIC without destruction of the device structure. From EBIC observation, bright spots with higher signal intensity than these in surrounding region are observed in p–n diodes, and these spots strongly correlate with the leakage current. It is found that these bright spots are originating from pits of comet‐shaped defects observed by a scanning electron microscope. With C‐AFM, the leakage current is detected at pits of comet‐shaped defects. Reduction in comet‐shaped defects shall be reduced using the technique of reduction in dislocation and high‐quality crystal growth to suppress the leakage current.