An array of CMUT cells has a DC bias voltage coupled to the top electrodes of the cells to bias the electrode to a desired collapsed or partially collapsed state. In the event of a short-circuit failure of a CMUT cell a protection circuit for the cell senses an over-current condition and responds by opening the DC current path through the failed cell. The protection circuit further disables the transmit and receive circuitry of the cell. In another implementation a sense circuit senses an over-current condition of the
DC bias supply and responds by disabling all of the CMUT cells of the array, then sequentially re-enabling them, except that an attempt to re-enable a failed cell results in that cell remaining in a disabled state.