Disclosed herein are a mask for forming a landing plug contact hole to vertically expose an active region of a semiconductor substrate to a bit line or storage node contact, and a plug forming method using the same. Through the use of the crescent-shaped masks, it is possible to increase the critical dimension at a lower end of the resultant contact hole in contact with an active region of a semiconductor substrate, thereby enabling exposure of a wider area of the active region to be connected with the bit line or storage node contact.