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The effects of thermal annealing on stacking faults and dislocations in single-crystal diamonds with a low defect density were investigated by synchrotron X-ray topography. We compared the X-ray topography images before and after annealing under various diffraction conditions. We found that the stacking faults disappeared after annealing, and new dislocations appeared at the edges of disappeared stacking faults. These results indicate that the stacking faults were Shockley type, and they were sandwiched between two Shockley partial dislocations. Therefore, we concluded that the Shockley stacking faults disappeared as a result of the movement of the Shockley partial dislocations. Before annealing, the perfect dislocations were straight along the [2 1 ¯ 1] direction; annealing caused these dislocations to bend along the [1 1 ¯ 0] and [101] directions. We identified two dislocation shapes; upper bending and lower bending dislocations. An analysis based on contrast extinction criterion; indicated that the bending direction depends on the Burgers vector, for example, a dislocation with b = a/2[101] moved along the [0 11 ¯ ] direction, and a dislocation with b = a/2[1 1 ¯ 0] moved along the [011] direction. [ABSTRACT FROM AUTHOR]