The performance benefits of a monolithically stacked 3D-FPGA, whereby the programming overhead of an FPGA is stacked on top of a standard CMOS layer containing the logic blocks and interconnects, are investigated. A Virtex-II style 2D-FPGA fabric is used as a baseline for quantifying the relative improvements in logic density, delay, and power consumption achieved by such a 3D-FPGA. It is assumed that only the pass-transistor switches and configuration memory cells can be moved to the top layers and that the 3D-FPGA employs the same logic block and programmable interconnect architecture as the baseline 2D-FPGA. Assuming a configuration memory cell that is ≤ 0.7 the area of an SRAM cell and pass-transistor switches having the same characteristics as nMOS devices in the CMOS layer are used, it is shown that a monolithically stacked 3D-FPGA can achieve 3.2 times higher logic density, 1.7 times lower critical path delay, and 1.7 times lower total dynamic power consumption than the baseline 2D-FPGA fabricated in the same 65nm technology node.