A semiconductor device includes an alignment key on a substrate. The alignment key includes a first sub-alignment key pattern with a first conductive pattern, a second conductive pattern, and a capping dielectric pattern that are sequentially stacked on the substrate, an alignment key trench that penetrates at least a portion of the first sub-alignment key pattern, and a lower conductive pattern in the alignment key trench. The alignment key trench includes an upper trench that is provided in the capping dielectric pattern that has a first width, and a lower trench that extends downward from the upper trench and that has a second width less than the first width. The lower conductive pattern includes sidewall conductive patterns that are separately disposed on opposite sidewalls of the lower trench.