The power efficiency of source-coupled logic (SCL) topology for implementing ultra-low-power and low-activity-rate circuits is investigated. It is shown that in low-activity-rate circuits, where the subthreshold leakage consumption of conventional CMOS circuits is more pronounced, subthreshold SCL (STSCL) can be used effectively for reducing the power consumption. An STSCL-based static random-access memory (SRAM) array has been implemented to demonstrate the performance of this topology for ultra-low-power consumption and low-activity-rate digital circuits. A novel 9T memory cell has been developed to reduce the stand-by (leakage) current to 10pA/cell while the SRAM array is operating at 2.1MHz clock frequency. The power consumption benefits of the proposed circuit style can be maintained in nanometer CMOS technology nodes.