Abstract: A method of manufacturing semiconductor devices includes forming a tunnel insulating layer, a conductive layer for a floating gate, and a hard mask layer on a semiconductor substrate, forming a first trench in the semiconductor substrate by partially etching the hard mask layer, the conductive layer for the floating gate, the tunnel insulating layer, and the semiconductor substrate, forming a first ion implantation region having a first impurity concentration into the semiconductor substrate of inner walls of the first trench by performing a first ion implantation process, forming a second trench extending from the first trench by etching the semiconductor substrate of a bottom of the first trench, and forming a second ion implantation region having a second impurity concentration lower than the first impurity concentration into the semiconductor substrate of inner walls of the second trench by performing a second ion implantation process, wherein a depth of the first trench is shallower than that of a juncti