A semiconductor device includes a device; a bonding oxide; and a carrier wafer bonded to the device through the bonding oxide. The carrier wafer includes a device area overlapped by the device in a plan view. The carrier wafer further includes an edge area adjacent to an outermost periphery of the carrier wafer, wherein the edge area has a first thickness. The carrier wafer further includes a non-bonding area between the device area and the edge area, wherein the non-bonding area has a second thickness greater than the first thickness, a first width of the non-bonding area is greater than a second width of the edge area, and the non-bonding area is free of an overhang structure.