Stacking faults (SFs) in a (111) single crystal diamond grown on a (111) seed crystal were investigated by taking synchrotron X-ray topography images with various diffraction vector g conditions. We found that the SFs on the {111} plane of fault vector f were a/3[11 (1) over bar], a/3[1 (1) over bar1], and a/3[111]. Subsequently, we analyzed these images in terms of the b-g extinction criteria and determined that the partial dislocations of the SFs were Shockley partial dislocations with Burgers vector b = a/6 < 211 >. Then, we determined that the SFs are Shockley type faults. Therefore, we propose that these SFs were generated by decomposition of one perfect dislocation with b = a/2<<(1)over bar>10>.