This paper presents a method based on dual threshold voltage assignment to reduce the leakage power dissipation of SRAMs while maintaining their performance. The proposed method is based on the observation that the read and write delays of a memory cell in an SRAM block depend on the physical distance of the cell from the sense amplifier and the decoder. The key idea is thus to realize and deploy different types of six-transistor SRAM cells corresponding to different threshold voltage assignments for individual transistors in the cell. Unlike other techniques for low-leakage SRAM design, the proposed technique incurs no area or delay overhead. In addition, it results only in a slight change in the SRAM design flow. Finally, it improves the static noise margin under process variations. Experimental results show that this technique can reduce the leakage-power dissipation of a 64Kb SRAM by more than 35%.