Abstract: A method for fabricating a CMOS image sensor which reduces occurrence of a dark current. The method includes forming a photodiode in a semiconductor substrate, forming an insulating film over and contacting the semiconductor substrate and the photodiode, respectively, forming a hard mask film over and contacting the insulating film, exposing an area of the insulating film corresponding spatially to the photodiode by performing a first etching process on the hard mask film, and then forming a trench in the insulating film by performing a second etching process using the etched hard mask film as a mask.