Methods of fabricating semiconductor devices may include forming a stopper layer, a lower hard mask layer, an intermediate hard mask layer, and an upper hard mask pattern on a substrate, forming first spacer patterns on sidewalls of the upper hard mask pattern, selectively etching the intermediate hard mask layer using the first spacer patterns as an etching mask, forming second spacer patterns on sidewalls of the etched intermediate hard mask layer, selectively etching the lower hard mask layer using the etched second spacer layer as an etching mask, forming a patterning mask pattern that exposes a cell area and covers a common source line area on the etched lower hard mask layer and the stopper layer, and selectively etching the stopper layer using the etched lower hard mask layer and the patterning mask pattern as etching masks to form stopper patterns.