One embodiment of the instant disclosure provides a semiconductor structure that comprises: a first device layer including a first active layer disposed over a substrate and a first gate layer disposed on the active layer, where at least one of the first active layer and the first gate layer includes a first layer alignment structure; a first bounding layer disposed over the first device layer, the first bounding layer including an opening arranged to detectably expose the first layer alignment structure; and a second device layer disposed over the bounding layer including a second layer alignment structure, where the second layer alignment structure is substantially aligned to the first layer alignment structure through the opening.