A method of manufacturing a semiconductor memory device, the method including forming a tunnel insulation layer on a substrate, forming a preliminary charge trapping layer on the tunnel insulation layer, forming an etch stop layer on the preliminary charge trapping layer, wherein a portion of the preliminary charge trapping layer is not covered by the etch stop layer, removing the exposed portion of the preliminary charge trapping layer to form a charge trapping layer having a uniform thickness, forming a dielectric layer on the charge trapping layer, and forming a gate electrode on the dielectric layer.