A doping method that forms a doped region at a desired location of a three-dimensional (3D) conductive structure, controls the doping depth and doping dose of the doped region relatively easily, has a shallow doping depth, and prevents a floating body effect. A semiconductor device is fabricated using the same doping method. The method includes, forming a conductive structure having a sidewall, exposing a portion of the sidewall of the conductive structure, and forming a doped region in the exposed portion of the sidewall by performing a plasma doping process.