A semiconductor structure includes a first substrate, a second substrate, a metal layer, a buffer structure, and a barrier structure. The first substrate has a landing pad. The second substrate is disposed over the first substrate. The metal layer is disposed in the second substrate and extends from the landing pad to a top surface of the second substrate. The buffer structure is disposed in the second substrate and surrounded by the metal layer, in which a top surface of the buffer structure is below a top surface of the metal layer. The barrier structure is disposed over the metal layer and the buffer structure.