A method for forming a plurality of gate patterns in parallel with each other on a photoresist layer within a circuit block includes forming extension gate patterns on both ends of the gate patterns and on both ends of a dummy gate pattern of the circuit block to reach an edge of the circuit block, and performing a first photolithography process upon the photoresist layer by using a phase shift photomask having first and second openings whose difference in phase is π, the first and second openings alternating between the gate patterns including the extension gate patterns to form phase edges therein.