To decrease grinding scratches by a method wherein a laser irradiates a backside of a wafer ground so as to reach a predetermined thickness by a whetstone, so that the surface is partially molten.

Grinding scratches occurred in grinding are left behind on a backside of a semiconductor chip, and a semiconductor chip 4 is mounted on a stand having a clearance of 10 mm, and a force is applied on a center part of the chip to acquire a magnitude of a force when the semiconductor chip is broken, and when transverse strength of the semiconductor chip is measured, it is made clear that each depth of scratches influences the transverse strength. A laser irradiates backside of a wafer ground so as to reach a predetermined thickness by a whetstone to melt the surface partially. More specifically, a YAG laser 2 is irradiated on the back surface of a wafer 1 while scanning. The irradiated semiconductor chip is cut out, and when the transverse strength is measured, the grinding scratches are flattened by laser irradiation to be in a substantially mirror face, and it is realized that the transverse strength is enhanced.