Power-gating has been widely used to reduce subthreshold leakage current. However, the extent of leakage saving through power-gating diminishes with technology scaling due to gate leakage of data-retention circuit elements. Furthermore, power-gating involves substantial increase of area and wirelength. A circuit technique called supply switching with ground collapse (SSGC) has recently been proposed to overcome the limitation of power-gating. The circuit technique is successfully applied to the register file of ARM9 microprocessor in a 1.2 V, 65-nm CMOS process, and the measured result is reported for the first time. The leakage current is reduced by a factor of 960 on average of 83 dies at 25??C , and by a factor of 150 at 85??C. Compared to a register file implemented in conventional power-gating, leakage current is cut by a factor of 2.2, demonstrating that SSGC can be a substitute for power-gating in nanometer CMOS.