A semiconductor device is provided, which, when cutting a substrate formed with a multilayer part including a plurality of functional devices, makes it possible to cut the multilayer part with a high precision in particular. In a state where a protective tape 22 is attached to the front face 16a of a multilayer part 16, a substrate 4 is irradiated with laser light L while using its rear face 4b as a laser light entrance surface, so as to form a modified region 7 within the substrate 4 along a line to cut, thereby generating a fracture 24 reaching the front face 4a of the substrate 4 from a front-side end part 7a of the modified region 7. Attaching an expandable tape to the rear face 4b of the substrate 4 and expanding it in the state where such a fracture 24 is generated can cut not only the substrate 4 but also the multilayer part 16 on the line to cut, i.e., interlayer insulating films 17a, 17b, with a favorable precision along the line to cut.