Abstract—This paper presents a new technique, called sub-clock power gating, for reducing leakage power in digital circuits. The proposed technique works concurrently with voltage and frequency scaling and power reduction is achieved by power gating within the clock cycle during active mode unlike traditional power gating which is applied during idle mode. < Final Year Projects > The proposed technique can be implemented using standard EDA tools with simple modifications to the standard power gating design flow. Using a 90nm technology library, the technique is validated using two case studies: 16-bit parallel multiplier and ARM Cortex-M0™ microprocessor, provided by our industrial project partner. Compared to designs without sub-clock power gating, in a given power budget, we show that leakage power saved allows 45× and 2.5× improvements in energy efficiency in the case of multiplier and microprocessor, respectively.