A micromachined ultrasonic droplet generator is demonstrated for drop-on-demand atomization of liquids for fuel processing. The device comprises a bulk ceramic piezoelectric transducer for ultrasound wave generation, a reservoir for the fuel, and a silicon micromachined array of liquid horn structures as the ejection nozzles. The droplet generator utilizes piezoelectric actuation combined with cavity resonances and acoustic wave focusing yielding low power consumption. A high degree of control of the atomization process and highly uniform atomization at low flow rates are achieved with a device that is extremely simple to fabricate, assemble, and operate. In addition, this technology allows one piezoelectric actuator to drive multiple ejectors of a single array so that the array size can be scaled to meet flow rate requirements. Device operation is demonstrated by droplet ejection from 5 – 10 µm orifices at multiple frequencies between 1 and 5 MHz.