A novel ultra-wideband (UWB) pulse synthesizer is proposed, which uses a distributed amplifier to combine Gaussian pulses of different polarities, amplitudes and delays. The center frequency and bandwidth of the synthesized pulse can be adjusted by varying the number of the Gaussian pulses and the delays between them. Compared to other UWB pulse generators, the present synthesizer is capable of higher voltages and higher efficiencies. Using 0.25-μm pHEMTs, a prototype synthesizer has been designed and fabricated with a center frequency of 4.0 GHz and a bandwidth of 1.9 GHz. Under a Gaussian input pulse of 1.5 V and 100 ps, the synthesizer outputs into 50 Ω a pulse of 4.5 V and 1 ns. At a pulse-repetition frequency of 10 MHz, the synthesizer consumes 1 mA at 3 V with 17% efficiency. Approaches to maintain high efficiency by scaling the supply voltage for different input amplitudes and pulse-repetition frequencies have also been verified experimentally.