A 3D interconnect structure comprising an ultra-thin interposer having a plurality of ultra-high density of through-via interconnections defined therein. The 3D interposer electrically connects first and second electronic devices in vertical dimension and has the same or similar through-via density as the first or second electronic devices it connects. The various embodiments of the interconnect structure allows 3D ICs to be stacked with or without TSVs and increases bandwidth between the two electronic devices as compared to other interconnect structures of the prior art. Further, the interconnect structure of the present invention is scalable, testable, thermal manageable, and can be manufactured at relatively low costs. Such a 3D structure can be used for a wide variety of applications that require a variety of heterogeneous ICs, such as logic, memory, graphics, power, wireless and sensors that cannot be integrated into single ICs.