A non-volatile memory device includes a semiconductor substrate having a first section including a substantially planar first top surface, a second section including a substantially planar second top surface, and a sidewall extending between the first and second top surfaces. The second top surface of the substrate is closer to a bottom surface of the substrate than is the first top surface. A charge storage pattern extends on the first and second top surfaces of the substrate and along the sidewall therebetween. A source region in the first section of the substrate extends from the first top surface into the second section of the substrate and has a stepped portion defined by the sidewall and the second top surface. Related fabrication methods and methods of operation are also discussed.