An image sensor and a method of fabricating the image sensor, the image sensor including a semiconductor substrate having a first floating diffusion region, a molding pattern over the first floating diffusion region and including an opening, a first photoelectric conversion part at a surface of the semiconductor substrate, and a first transfer transistor connecting the first photoelectric conversion part to the first floating diffusion region. The first transfer transistor includes a channel pattern in the opening and a first transfer gate electrode. The channel pattern includes an oxide semiconductor. The channel pattern also includes a sidewall portion that covers a side surface of the opening, and a center portion that extends from the sidewall portion to a region over the first transfer gate electrode.