MEMS ultrasonic sensor was fabricated using the poly(vinylidene fluoride-trifluoroethylene)[P(VDF/TrFE)] copolymer thin films having multilayer diaphragm structures. It was shown that the P(VDF/TrFE) thin film on MEMS ultrasonic sensor exhibit a remanent polarization P_r of 72 mC/m² and a coercive field E_c of 59 MV/m. The resonant frequency, Q-value and sensitivity of the MEMS ultrasonic sensors are estimated to be on the order of 178 kHz, 24 and 45 µV/Pa, respectively. The P(VDF/TrFE) thin film was shown to be useful for piezoelectric material of MEMS ultrasonic sensor.