PURPOSE: To provide a method for machining a semiconductor ingot into a required semiconductor wafer through a slicing step and a lapping step in which the warp of the wafer can be reduced significantly.

CONSTITUTION: The surface and the rear of a wafer are previously machined into a convex or concave shape during the slicing step. As shown in Fig.A, the surfaces of wafers 1, 2 are abutted on a lapping surface plate from the central part or the peripheral part thereof at the time of lapping thus preventing the elastic deformation at the time of lapping. Since the wafers are cut off starting from the part abutting on the lapping surface plates 3, 4, a water B having suppressed warp can be formed as shown in fig. B.