Micromachined ultrasonic transducers having pressure ports are described. The micromachined ultrasonic transducers may comprise flexible membranes configured to vibrate over a cavity. The cavity may be sealed, in some instances by the membrane itself. A pressure port may provide access to the cavity, and thus control of the cavity pressure. In some embodiments, an ultrasound device including an array of micromachined ultrasonic transducers is provided, with pressure ports for at least some of the ultrasonic transducers. The pressure ports may be used to control pressure across the array.