Provided is a treatment method of a semiconductor wafer facilitating picking-up of semiconductor chips and preventing contamination by a dicing sheet. A wafer back surface treating method is characterized in that a ground or polished surface of a semiconductor wafer activated in a grinding or polishing step, with semiconductor circuits formed thereon, is deactivated. In the method, the activation treatment with an oxidizing agent is preferable. Furthermore, the activation treatment is preferably implemented with blowing of ozone to a ground or polished surface of a wafer, with ozone water or with illumination of a ground or polished surface of a wafer with ultraviolet (UV). It is preferable to adhere a dicing sheet after the deactivation treatment.