Size-controlled porous silicon-based nanoparticles are prepared by pulsed electrochemical etching of single crystal silicon wafers, followed by ultrasonic fracture of the freestanding porous layer. When high-current density pulses are applied periodically during the porous layer etching process, a porous multilayer results in which porous layers are separated by thin layers of much higher porosity. Ultrasonic fracture selectively cleaves the porous film along these high-porosity perforations, providing greater size control and improved yields (by 5x) of the resulting porous nanoparticles. The effect of pulse width and repetition rate is systematically studied: tunability of the average nanoparticle size in the range 160-350 nm is demonstrated.