A mask layout for forming a semiconductor device includes an active mask pattern, a gate electrode mask pattern, a silicide blocking mask pattern, and a contact mask pattern. The active mask pattern forms source and drain regions in a substrate. The gate electrode mask pattern, disposed to overlap the active mask pattern, forms a gate electrode between the source region and the drain region. The silicide blocking mask pattern is disposed to overlap the gate electrode mask pattern and the active mask pattern in the gate electrode, the source region, and the drain regions to form a silicide blocking region. The contact mask pattern, disposed spaced apart from the silicide blocking mask pattern, forms a contact plug on the substrate. The silicide blocking mask pattern covers the gate electrode mask pattern and extends to the active mask pattern.