A method of fabricating a semiconductor device includes: (i) placing, on a first layout, first patterns that extend parallel to each other in a first direction and are spaced apart from each other in a second direction intersecting the first direction, (ii) extracting a low-density region on the first layout, (iii) defining an enclosure region that surrounds the first patterns, (iv) placing dot patterns on a second layout, (v) extracting, from the dot patterns, first dot patterns that overlap the low-density region and do not overlap the enclosure region, (vi) placing the extracted first dot patterns on the first layout, (vii) allowing the first dot patterns to extend in the first direction to form second patterns, and (viii) using the first and second patterns to respectively form first and second active patterns on a substrate.