The invention provides a method for fabricating a fin field effect transistor (FinFET), comprising: providing a substrate having a logic region and a large region; forming a plurality of fin structures in the logic region by removing a portion of the substrate in the logic region; forming an oxide layer on the substrate filling in-between the fin structures in the logic region; forming an first epitaxial structure in the large region by removing a portion of the substrate in the large region; exposing a portion of the fin structures and a portion of the epitaxial structure by removing a portion of the oxide layer; and forming a gate electrode on portions of the fin structures.