In a device processing method, a laser beam is applied to a wafer along division lines from the back side of the wafer, thereby forming a division start point inside the wafer along the division lines at a depth not reaching the finished thickness of each device. A protective member is attached to the front side of the wafer before or after performing the division start points are formed. An external force is applied through the protective member to the wafer, thereby dividing the wafer along the division lines to obtain the individual devices. The back side of the wafer is ground to remove the modified layers, and a silicon nitride film is formed on at least the side surface of each device. The silicon nitride film has a gettering effect and is formed on the side surface of each device, which surface is formed by a cleavage plane.