Provided is an electrostatic discharge (ESD) protection diode including: a well formed of a first conductivity in a semiconductor substrate; an active region that is formed of a second conductivity in the well and includes a plurality of first active lines extending in a first direction; a sub-region of the first conductivity including a plurality of first sub-lines extending in the first direction, the first sub lines being formed in the well, arranged to surround an outer region of the first active lines, and arranged in alternation with the first active lines; a device isolation region separating the active regions and the sub-regions; a plurality of active contacts arranged in a row in the active regions; and a plurality of sub-contacts arranged in a row in the sub-region.