It is shown that the acoustic pulse output of nanocrystalline porous silicon (nc-PS) ultrasonic emitter can be enhanced by appropriate control of both the driving mode and the nc-PS structure. The device is composed of a patterned heater electrode, an nc-PS layer, and a single-crystalline silicon (c-Si) substrate. As the sound pressure is proportional to input power in principle, the nc-PS device can generate a high acoustic power under the mode of temporal burst electrical input. The most important limiting factor for maximum electrical input power is a mechanical stress at the electrode/nc-PS interface induced by a rapid interfacial temperature raise rather than a simple electro-migration inside the thin metal film. In fact the maximum sound pressure is enhanced with increasing the hardness and Young's modulus of the nc-PS layer. The present result provides useful information for further progress of the nc-PS acoustic device.