A method of fabricating a single diffusion break includes providing a fin with two gate structures crossing the fin and a middle dummy gate structure crossing the fin, wherein the middle dummy gate structure is sandwiched by the gate structures. Later, numerous spacers are formed and each spacer respectively surrounds the gate structures and the middle dummy gate structure. Then, the middle dummy gate structure, and part of the fin directly under the middle dummy gate structure are removed to form a recess. Finally, an isolating layer in the recess is formed to close an entrance of the recess so as to form a void embedded within the recess.