Abstract: A CMOS image sensor and a manufacturing method are disclosed. The gates of the transistors are formed in the active region of the unit pixel, and a diffusion region for the photo diode is defined by an ion implantation of impurities to the semiconductor substrate. The patterns of the photoresist that are the masking layer against ion implantation are formed on the semiconductor substrate in such a manner that they have the boundary portion of the isolation layer so as not to make the boundary of the defined photo diode contact with the boundary of the isolation layer. Damages by an ion implantation of impurities at the boundary portion between the diffusion region for the photo diode and the isolation layer are prevented, which reduces dark current of the COMS image sensor.