We present an area- and power-efficient application-specific integrated circuit (ASIC) for a miniaturized 3-D ultrasound system. The ASIC is designed to transmit pulse and receive echo through a 36-channel 2-D piezoelectric Micromachined Ultrasound Transducer (pMUT) array. The 36-channel ASIC integrates a transmitter (TX), a receiver (RX), and an analog-to-digital converter (ADC) within the 250-mu m pitch channel while consuming low-power and supporting calibration to compensate for the process variation of the pMUT. The charge-recycling high-voltage TX (CRHV-TX) in standard CMOS generates up to 13.2-VPP pulse while reducing 42.2% peak TX power consumption. Also, each CRHV-TX automatically calibrates excitation voltage according to acoustic pressure of pMUT. The dynamic-bit-shared ADC (DBS-ADC) shares the most significant bits (MSBs) among four channels based on the signal similarity between adjacent channels. The analog front end (AFE) with a received signal sensitivity indicator (RSSI) changes its gain adaptively in real time depending on input signal strength. The ASIC consumes 1.14-mW/channel average power with 1-kHz pulse repetition frequency (PRF) and three TX pulses per cycle. The ASIC in 0.18-mu m 1P6M Standard CMOS has been verified with both electrical and acoustic experiments with a 6x6 pMUT array.