To provide a method for dividing a semiconductor wafer (2) with sufficient precision along a street (10), utilizing a laser beam (18) while sufficiently avoiding/suppressing contamination of a circuit (14) formed in a rectangular region (12) on the surface (8) without causing any break in the rectangular region on the surface.

A laser light beam is irradiated from the rear surface (20) side or the surface (8) side of a semiconductor substrate (4) and condensed on the surface or rear surface of the semiconductor substrate and the vicinity thereof, thus deteriorating the semiconductor substrate up to a specified depth at least from the surface or the rear surface.