Sleep transistors such as MTCMOS and SCCMOS drastically reduce leakage current, but their ON resistances cause significant performance degradation. Larger sleep transistors reduce their ON resistances, but increase leakage current in a sleep mode. Decoupling capacitors beside sleep transistors reduce leakage current. Experimental results show that PMOS SCCMOS with a 4 pF decoupling capacitor reduces leakage current by 1/673 on a 64 bit adder in a 90 nm process.