The invention discloses an ultrasonic sensor comprising a substrate, a plurality of pixel electrodes, a piezoelectric sheet, a conductive electrode and a processing chip. A plurality of pixel electrodes are fabricated on the substrate and distributed in an array. A piezoelectric sheet is provided on the substrate and covers a plurality of pixel electrodes, the piezoelectric sheet is used for emitting ultrasonic waves and generating an electrical signal after receiving the ultrasonic waves reflected by the object to be detected, and the plurality of pixel electrodes are used for receiving the electrical signal. The conductive electrode is arranged on a piezoelectric sheet, and the piezoelectric sheet is positioned between the pixel electrode and the conductive electrode. The processing chipis connected with a plurality of pixel electrodes, and is used for processing an electrical signal to form an ultrasonic image of an object to be detected. As each pixel electrode can determine the position of the finger pressed on the ultrasonic sensor and the electric signal generated by the piezoelectric plate at the position according to the received electric signal, the amount of data to beprocessed by the processing chip is reduced, and the recognition efficiency of the ultrasonic sensor is improved. The invention also discloses an electronic device.