In a semiconductor device, a metal wiring film and a lower-layer film under a bump electrode are patterned to form irregular steps under the bump electrode. With the formation of the irregular steps, the contact area of the bump electrode with a semiconductor substrate is increased to improve the mechanical strength. The lower-layer film is formed of a polysilicon film, an insulating film or a protective film such as a silicon nitride film, or Al--Si--Cu, Al--Si, Al--Cu or Cu. A portion where irregular steps are formed is in a region under the bump except for a protective film opening portion.