A nonvolatile memory device includes a semiconductor substrate, a device isolation layer, a tunnel insulation layer, a floating gate, a buried floating gate, and a control gate. A trench is in the substrate that defines an active region of the substrate adjacent to the trench. A device isolation layer is on the substrate along the trench. A tunnel insulation layer is on the active region of the substrate. A floating gate is on the tunnel insulation layer opposite to the active region of the substrate. A buried floating gate is on the device isolation layer in the trench. An intergate dielectric layer is on and extends across the floating gate and the buried floating gate. A control gate is on the intergate dielectric layer and extends across the floating gate and the buried floating gate.