Methods of fabricating semiconductor device are provided including forming first through third silicon crystalline layers on first through third surfaces of an active region; removing the first silicon crystalline layer to expose the first surface; forming a bit line stack on the exposed first surface; forming bit line sidewall spacers on both side surfaces of the bit line stack to be vertically aligned with portions of the second and third silicon crystalline layers of the active region; removing the second and third silicon crystalline layers disposed under the bit line sidewall spacers to expose the second and third surfaces of the active region; and forming storage contact plugs in contact with the second and third surfaces of the active region.