A semiconductor device includes a semiconductor substrate having a bonding pad, and a first dielectric layer disposed over the semiconductor substrate. A portion of the bonding pad is exposed by the first dielectric layer. The semiconductor device also includes a metal oxide layer disposed over the portion of the bonding pad, and a wire bond penetrating through the metal oxide layer to bond to the bonding pad. The portion of the bonding pad is entirely covered by the metal oxide layer and the wire bond.