An image sensor and a method of fabricating the same are disclosed. The image sensor may include a substrate including an active region defined by a device isolation layer, a photoelectric conversion layer, a well impurity layer, a floating diffusion region, and a transfer gate. When viewed in a plan view, a lower portion of the transfer gate may include a first surface in contact with the device isolation layer, a second surface substantially perpendicular to the first surface, and a third surface connected to the first and second surfaces. The third surface may face the floating diffusion region. A first portion of a gate insulating layer may be adjacent to the third surface and thinner than a portion adjacent to the first surface or the second surface, and this may facilitate more efficient transfer of an electron from the photoelectric conversion layer to the floating diffusion region.