We have developed a technique of on-chip multisite acoustofluidic manipulation using aluminum nitride on silicon (AlN-on-Si) piezoelectric micromachined ultrasonic transducers (PMUTs). We demonstrate nine-channel acoustically driven particle enrichment on a 3times 3 PMUT array fabricated on a micromachined chip by simply exciting a single PMUT. Adding a micro-oil droplet to just one PMUT enables the multichannel particle enrichment and stirring simultaneously. Compared with the larger surface acoustic wave (SAW) devices, the proposed acoustic tweezing method enabled by plane waves generated from the PMUT presents unique merits: 1) highly localized particle manipulation directly on the PMUTs; 2) the ability to manipulate particles in arrays at chip scale; and 3) synchronous dual-function particle manipulation modes driven by a single device within the chip. These unique features render the possibility of integrated circuit compatible acoustofluidics for high throughput bead-based bioassays in lab-on-a-chip (LOC) platforms.