Abstract This paper describes a piezoelectric microphone built on a circular diaphragm (CD), which is fabricated using the boron etching stop method. ZnO was used as the piezoelectric material, and the diaphragm material is low-stress Si x N y . The diameter and thickness of the circular diaphragm are 2 mm and 1 μm, respectively. The thickness of the boron-doped layer – a support layer for the circular diaphragm – is approximately 7.4 μm. Based on ANSYS simulations, the sensitivity increment of the CD microphone was comparable to that of a square diaphragm (SD) microphone. The sensitivity of the CD microphone increased to 197% of that of a SD microphone, as expected from the simulation results. The first resonance frequency of the CD microphone is 54.8 kHz. At 1 kHz, the displacement of the CD microphone and SD microphone are 3.96 nm and 1.54 nm, respectively. The fabricated CD microphone was connected to an amplifier system to confirm the ability to reproduce a human voice. The gain of the amplifier system is 200.