Experimental results are reported on the speed/power performance of normally-off-type GaAs-m.e.s.f.e.t. logic circuits, using an integrated 15-stage ring oscillator as a test circuit. A power consumption as low as 1-5 μW, corresponding to a power-delay product of 1.6 fJ, was obtained. Conversely, a propagation delay time of 650 ps was measured for a power consumption of 20 μW per gate.