Wafer processing method capable of reducing cost while the convex/concave of a bulge won't be transferred to a polished face

Provided is a wafer processing method capable of reducing cost while the convex/concave of a bulge won't be transferred to a polished face even though the height of the bulge is relatively high, the thickness difference of a polished wafer will be reduced, chip collision will be prevented during a polishing process, and the leakage of a negative pressure won't occur when holding the wafer at a clamping-tray carrying table. A wafer processing method is a processing method to cut a wafer along predetermined cutting lines and form a plurality of chips of prescribed thickness, in which elements are formed in each field of a surface that is divided by the predetermined cutting lines formed in a cross pattern, and each element has a plurality of bulges protruding toward the surface. The method is characterized by comprising: a trench forming step forming trenches on the surface of the wafer along the predetermined cutting lines while the thickness of the trenches is deeper than the prescribed thickness and not suff