A semiconductor device is provided and includes first and second semiconductor chips bonded together. The first chip includes a first substrate, a first insulating layer disposed on the first substrate and having a top surface, a first metal pad embedded in the first insulating layer and having a top surface substantially planar with the top surface of the first insulating layer, and a first barrier disposed between the first insulating layer and the first metal pad. The second chip includes a second substrate, a second insulating layer, a second metal pad, and a second barrier with a similar configuration to the first chip. The top surfaces of the first and second insulating layers are bonded to provide a bonding interface, the first and second metal pads are connected, and a portion of the first insulating layer is in contact with a side region of the first metal pad.