A semiconductor memory device comprising: a support substrate; an insulating film formed on the support substrate; a semiconductor film formed on the insulating film; a gate insulating film formed on the semiconductor film; a gate electrode film formed on the gate insulating film; and a source region and a drain region formed in the semiconductor film so as to sandwich the gate insulating film in a gate length direction, the source and drain regions contacting the insulating film at the bottom surface, and the semiconductor memory device storing data corresponding to the amount of charges accumulated in the semiconductor film surrounded by the insulating film, the gate insulating film, and the source and drain regions and electrically floated, wherein a border length between the source region and the gate insulating film contiguous to each other is different from a border length between the drain region and the gate insulating film to each other.