An image sensor includes defining an active region in a substrate by forming a device isolating layer; and then sequentially forming a photodiode and a logic unit in the active region; and then forming a first passivation layer on the photodiode and the logic unit; and then forming a trench in the first passivation layer by selectively removing a portion of the first protective layer corresponding to an uppermost surface of the photodiode; and then forming a second passivation layer buried in the trench. Forming a thick second passivation layer in the trench which spatially corresponds to the photodiode can offset dangling bonds on the surface of the substrate in a subsequent annealing process while also reducing dark current and enhance photosensitivity of the photodiode.