That's going to require some rather expensive hardware.
"Having an ASIC fabricated is a highly technical and expensive proposition, typically beginning at the low hundreds of thousands of dollars. That’s primarily because contractors—almost always overseas—charge high prices to operate facilities containing the complex equipment needed to carve chips out of silicon wafers. ASICs are etched from blocks of silicon with microscopic precision. Butterfly Labs says it has paid for chips with features as small as 65 nanometers; BTCFPGA and some others say they have opted for a cheaper 90-nanometer production process."
Building your own FPGA is feasible, but solder intensive:
https://bitcointalk.org/index.php?topic=44891
