Various embodiments provide semiconductor devices having cavity substrate structures for package-on-package assembly and methods for their fabrication. In one embodiment, the cavity substrate structure can include at least one top interconnect via formed within a top substrate. The top substrate can be disposed over a base substrate having at least one base interconnect via that is not aligned with the top interconnect via. Semiconductor dies can be assembled in an open cavity of the top substrate and attached to a base center portion of the base substrate of the cavity substrate structure. A top semiconductor package can be mounted over the top substrate of the cavity substrate structure.