The features of generation and motion of dislocations in nitrogen-doped dislocation-free silicon wafers after their multistage thermal treatments are investigated. It is established that doping with nitrogen leads to a substantial increase in stresses of the onset of plastic deformation from the external and internal heterogeneous sources in heat-treated wafers. The motion velocity of dislocations in nitrogen-doped silicon wafers is lower than in undoped wafers. The strengthening effect of nitrogen is apparently caused by its activating effect on the decomposition process of a supersaturated solid solution of oxygen during heat treatment.