A transistor having an electrode layer that can reduce or prevent a coupling effect, a fabricating method thereof, and an image sensor having the same are provided. The transistor includes a semiconductor substrate and a well of a first conductivity type formed on the semiconductor substrate. A heavily-doped first impurity region of a first conductivity type surrounds an active region defined in the well. Heavily-doped second and third impurity regions of a second conductivity type are spaced apart from each other in the active region an define a channel region interposed therebetween. A gate is formed over the channel region to cross the active region. The gate overlaps at least a portion of the first impurity region and receives a first voltage. An electrode layer is formed between the semiconductor substrate and the gate, such that the electrode layer overlaps a portion of the first impurity region contacting the channel region and receives a second voltage. An insulation layer is formed between the semiconductor substrate and the electrode layer, the semiconductor substrate and the gate, and the electrode layer and the gate. The insulation layer surrounds the electrode layer.