Disclosed here in is a method for patterning an active region in a semiconductor device using a space patterning process that includes forming a partition pattern having partition pattern elements arranged in a square shape on a semiconductor substrate; forming a spacer on side walls of the partition pattern; removing the partition pattern; separating the spacer into first and second spacer portions to expose a portion of the semiconductor substrate; and etching the exposed portion of the semiconductor substrate to form a trench, wherein portions of the semiconductor substrate overlapped with the first and second spacer portions define an active region.