The manufacturability of a lithographic mask employed in fabricating instances of a semiconductor device is determined. Target edge pairs are selected from mask layout data of the mask, for determining a manufacturing penalty in making the mask. The manufacturability of the mask, including the manufacturing penalty in making the mask, is determined based on the target edge pairs as selected, and is dependent on the manufacturing penalty in making the mask. Determining the manufacturability of the mask includes, for a selected edge pair having first and second edges that are at least substantially parallel to one another, determining a manufacturing shape penalty owing to an aspect ratio of the first edge relative to a size of a gap between the first edge and the second edge. This penalty takes into account a pair of connected edges of the first edge that are at least substantially parallel to the first edge.