Residual stresses in SiC wafers, which were introduced during production processes including sawing, lapping,mechanical polishing (MP), and chemical-mechanical polishing (CMP), were evaluated in terms of changes in radius of curvature and high-resolution X-ray diffractometer (HRXRD) measurements. It was found that annealing was an effective method to reduce stress fields and to improve the wafer flatness. Lapping process generated more residual stresses than other machining processes, and these stresses could be relaxed by thermal treatment. The results showed that annealing was an essential procedure following lapping in the whole production process. The molten KOH etching results accounted for the correlation between the relaxation of stresses and the creation of basal screw dislocations.