This article presents a new approach for improving the power-delay performance of subthreshold source-couple logic (STSCL) circuits. Using a simple two-phase pipelining technique, it is possible to increase the activity rate of STSCL gates with negligible additional cost, and hence reduce the total system energy consumption per operation. In the proposed pipelined topology, each STSCL gate is followed by a simple cross-coupled differential pair operating as a state keeper with a very low power consumption and small area overhead. Measurement results on a 32-bit pipelined adder chain fabricated with 0.18um CMOS technology show that the proposed approach can achieve a significant reduction in power-delay product (PDP) down to 5fJ/stage.