As a modified form of chemical vapor deposition (CVD) and electrochemical vapor deposition (EVD), polarized electrochemical vapor deposition (PEVD) utilizes a d.c. bias potential to create an electrochemical potential difference inside an ionic conductor under a polarized condition. The gas electrode reactions are then utilized to form new phases at the surface. The advantages of polarized electrochemical vapor deposition are not only based on the mechanism of PEVD product crystal growth, but also arise from the close control possible over the entire PEVD process. In this paper, PEVD is used to deposit a NaNO3 auxiliary phase for a potentiometric NO2 sensor.