A selectable, dual-frequency, capacitive micro- machined ultrasonic transducer (CMUT) designed for both high-frequency imaging and low-frequency therapeutic effect is presented. A validated finite element analysis (FEA) CMUT model was used to examine the performance of the proposed dual-frequency transducer. CMUT device simulations were used to design a hybrid device incorporating stand-off structures that divide a large, low-frequency membrane into smaller, high-frequency sub-membranes when the membrane is partially collapsed so that the stand-offs contact the substrate. In low-frequency operation, simulations indicated that the peak negative pressure achieved by the hybrid device, when biased by 30.0 VDC and excited by a 2-MHz signal with 30.0 V amplitude, exceeded 190 kPa, which is sufficient for microbubble rupture. Low-frequency mode bandwidth was 93% at a center frequency of 2.1 MHz. In the high-frequency mode of operation, the device was excited by 175 Vdc and 87.5 Vac, which generated a peak negative pressure of 247 kPa. Device center frequency was 44.1 MHz with a - 6-dB fractional bandwidth of 42%.