An image sensor includes a trench formed in a semiconductor substrate, a first reflection part formed in the trench and having an inclined, curved surface, a second reflection part formed on the first reflection part such that a remaining space of the trench is filled with the second reflection part, and a vertical type photodiode formed on a region of the substrate between trenches. A method for forming the image sensor includes forming a trench in a semiconductor substrate, forming a first reflection part having an inclined, curved surface in the trench, forming a second reflection part on the first reflection part such that a remaining space of the trench is filled with the second reflection part, and forming a vertical type photodiode on a region of the substrate between trenches.