a nonvolatile memory device Includes an active region defined in a semiconductor substrate and a control gate electrode crossing over the active region. A gate insulating layer is interposed between the control gate electrode and the active reigon. A floating gate is formed in the active region to penetrate the control gate electrode and extend to a predetermined depth into the semiconductor substrate. A tunnel insulating layer is successively interposed between the control gate electrode and the floating gate, and between the semiconductor substrate and the floating gate. The floating gate may be formed after a trench is formed by sequentially etching a control gate conductive layer and the semiconductor substrate, and a tunnel insulating layer is formed on the trench and sidewalls of the control gate conductive layer. The floating gate is formed in the trench to extend into a predetermined depth into the semiconductor substrate.