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We present a microelectromechanical systems (MEMS)-based electrostatic actuator on a flexible substrate, made of polyethylene naphthalate, which emits acoustic waves at ultrasonic frequencies. The actuator has a suspended diaphragm, made of parylene, of 2-6-mm diameter and a 6-μm gap between the diaphragm and substrate. The actuator is driven by hydrogenated amorphous silicon integrated circuits. The driving circuits consist of voltage-controlled oscillator and buffer chain, which can tune the output voltage from 3 to 32 V with 35-V supply. A single actuator emits ultrasonic waves at 25 kHz and pressure of 27-dB sound pressure level (SPL), and a 1 × 2 array emits up to 34.6-dB SPL at 1-cm distance.