A design structure embodied in a machine readable medium used in a design process includes a tri-state power gating apparatus for reducing leakage current in a memory array. The apparatus includes a first distributed header device coupled to the memory array, the first distributed header device is configured for limiting leakage current through the memory array; and a header driver operatively coupled to the first distributed header device for enabling tri-state operation of the first distributed header device, wherein tri-state operation includes sleep mode, wake mode, and retention mode.