A structure of semiconductor device is provided, including a first circuit structure, formed on a first substrate. A first test pad is disposed on the first substrate. A second circuit structure is formed on a second substrate. A second test pad is disposed on the second substrate. A first bonding pad of the first circuit structure is bonded to a second bonding pad of the second circuit structure. One of the first test pad and the second test pad is an inner pad while another one of the first test pad and the second test pad is an outer pad, wherein the outer pad surrounds the inner pad.