In this study, we successfully developed a high signal-to-noise ratio (SNR) rangefinder based on a piezoelectric micromachined ultrasonic transducer (pMUT). A monocrystalline Pb(Mn1/3, Nb2/3)O3-Pb(Zr, Ti)O3 (PMnN-PZT) thin film was used because it has large figures-of-merit (FOM) for SNR due to its high piezoelectric coefficient and small relative permittivity (typical values: e31,f = -14 C/m2, ϵr = 200∼300). The rangefinding ability of the monocrystalline PMnN-PZT pMUT was evaluated using a pair of the devices as transmitter and receiver. The maximum range was estimated to be over 2 m at a low actuating voltage of 1 Vp-p, when 12 dB was set as the threshold SNR for reliable rangefinding. The energy consumption of the transmitter was as small as ∼55 pJ for the generation of an ultrasonic burst. This performance is suitable for rangefinding applications in consumer electronics.