The electromechanical conversion efficiency and the long-term reliability of Capacitive Micromachined Ultrasonic Transducers (CMUT) are mainly limited by the parasitic capacitance and by charge injection phenomena, which are generated the first, by the portions of the CMUT electrodes used for interconnection, and the second, by the low dielectric strength of the in-cavity passivation materials. Reverse Fabrication Process (RFP) [doi: 10.1088/0960-1317/25/1/015012] is a sacrificial-release low-temperature CMUT technology that employs ultra-low-stress Silicon Nitride (Si _x N _y ) dielectrics and Titanium-Aluminum-Titanium metals. In this paper, we investigated the possibility of reducing both the parasitic capacitance, by acting on the electrodes layout, and the charge injection phenomena, by introducing Silicon Oxide (SiO ₂ ) buffer layers between the electrodes and the in-cavity passivation layers.