A method for forming FinFETs includes providing a semiconductor substrate having at least a first fin in a first region and at least a second fin in a second region, and a first gate structure over the first fin and a second gate structure over the second fin; forming a first stress layer on the first fin and a first cover layer on the first stress layer; forming a second stress layer on the second fin and a second cover layer on the second stress layer; performing a first potential barrier reducing ion implantation process on the first cover layer; performing a second potential barrier reducing ion implantation process on the second cover layer; forming a first metal layer and a second metal layer; and forming a first contact layer on the first cover layer and a second contact layer on the second cover layer.