A method for reducing cross talk in image sensors comprises providing a backside illuminated image sensor wafer, forming an isolation region in the backside illuminated image sensor wafer, wherein the isolation region encloses a photo active region, forming an opening in the isolation region from a backside of the backside illuminated image sensor wafer and covering an upper terminal of the opening with a dielectric material to form an air gap embedded in the isolation region of the backside illuminated image sensor wafer.