A nonintrusive three‐dimensional trap for microscopic particles in a liquid is described. The trap is based on acoustic radiation forces in an ultrasonic confocal standing‐wave cavity. Experiments at 11 MHz demonstrate the concept and verify the theoretically calculated forces. Theoretical calculations for higher‐frequency systems indicate a significant potential for low‐rms‐displacement trapping of submicrometer particles, making the trap suitable for nonintrusive scanning near‐field optical microscopy. ©1995 American Institute of Physics.