We report here an in situ method to monitor and optimize formation of thin semiconductor passive films of bismuth oxides and sulfides for enhanced photoelectrochemical performances. It was conducted by cyclic voltammetry under visible light illumination in a mixed solution of Na2SO3 and Na2S. Electrooxidation and sulfurization of Bi electrodes occurred simultaneously during the potential cyclings between -1 V and 0 V (vs. Hg vertical bar Hg2SO4(s)vertical bar K2SO4 (saturated)), and the semiconductor passive film with an appropriate thickness was formed effectively under light illumination. In comparison with the composite film of Bi2S3/Bi2O3 loaded on conductive glass, enhanced photoelectrochemical performances were observed in much wider potential ranges on the prepared semiconductor passive film due to its very compact coverage. Higher anodic photocurrent density was obtained from -1 V to 10 V on the semiconductor passive film prepared under light illumination than in dark, and under galvanostatic operation the anodic potential went back and forth between -1.1 V and 9.8 V rapidly while the visible light illumination was on and off. We expect that these photoelectrochemical characteristics will find applications in photoelectrochemical hydrogen production, photodetectors and photoswitches. (C) 2015 The Electrochemical Society.