A wafer level stack structure, including a first wafer including at least one first device chip of a first chip size, wherein each first device chip contains a first plurality of input/output (I/O) pads, a second wafer including at least one second device chip of a second chip size smaller than the first chip size, wherein each second device chip contains a second plurality of I/O pads, wherein the at least one second device chip is increased to the first chip size, wherein the first wafer and the second wafer are stacked, and wherein the first wafer and the second wafer are coupled to each other. A method of forming a wafer level stack structure, including forming a first wafer including at least one first device chip of a first chip size, wherein each first device chip contains a first plurality of input/output (I/O) pads, forming a second wafer including at least one second device chip of a second chip size smaller than the first chip size, wherein each second device chip contains a second plurality of I/O pads, wherein the at least one second device chip is increased to the first chip size, stacking the first wafer and the second wafer, and coupling the first wafer and the second wafer to each other. A system-in-package, including a wafer level stack structure including at least one first device chip with a first plurality of input/output (I/O) pads and at least one second device chip with a second plurality of I/O pads, and a common circuit board to which the wafer level stack structure is connected.