A first wafer includes a first semiconductor layer and first metal contacts on a side of a first surface of the first semiconductor layer. A second wafer includes a second semiconductor layer and second metal contacts on a side of a first surface of the second semiconductor layer. A handle is bonded onto a surface of the second wafer opposite to the second semiconductor layer. The second semiconductor layer is then removed to expose the second metal contacts. A bonding is then performed between the first and second wafers to electrically connect the first metal contacts to the second metal contacts.