An ultrasonic biometric sensor comprises a detection chip. The detection chip includes a substrate, an ultrasonic transducer array and a control circuit. The ultrasonic transducer array is arranged on the substrate, including a plurality of arrayed piezoelectric elements. Each piezoelectric element is disposed on a floating membrane. The floating membrane is suspended in the opening side of a cavity by at least one support arm extending transversely. The control circuit is also arranged on the substrate and electrically connected with each piezoelectric element through the support arm to control the ultrasonic transducer array to generate an ultrasonic signal and read the reflected ultrasonic signal received by the ultrasonic transducer array. The ultrasonic biometric sensor is easy to fabricate and has a high yield.