CMOS-based image sensors have recently emerged as strongest counterparts to CCDs (Charge Coupled Devices) thanks to great improvements in image quality. The CMOS-based image sensors are generally featured by (1) fast parallel readout, (2) low power consumption and (3) on-chip peripheral circuit capability. Also, for D-SLR (Digital-Single Lens Reflex) cameras, “stitching technology” allows only CMOS-based image sensors to provide practical 35mm-format imagers. The CMOS-based image sensors are starting to contend with CCDs in small pixels such as less than 3um. Different pixel shrinkage schemes have been proposed along with process design rule miniaturization. Market demands and intense competition will continue to be the main factors to drive the technologies of CMOS-based image sensors.