An image sensor includes a trench formed by a shallow trench isolation (STI) process, a channel stop layer formed over a substrate in the trench, an isolation structure filled in the trench, and a photodiode formed in the substrate adjacent to a sidewall of the trench. In more detail of the image sensor, a trench is formed in a substrate through a STI process, and a channel stop layer is formed over the substrate in the trench. An isolation structure is formed in the trench, and a photodiode is fanned in the substrate adjacent to a sidewall of the trench.