A pad structure includes a first metal-containing layer formed over a substrate. A first passivation layer is formed over the first metal-containing layer. The first passivation layer has a first opening partially exposing the first metal-containing layer. A pad layer is formed over the first passivation layer, covering the first opening. The pad layer includes a probing region configured to be contacted by a probe and a bonding region configured to have a wired bonded to it. The probing region contacts the first metal-containing layer through the first opening, and the bonding region overlies a portion of the first passivation layer.