A method for fabricating a semiconductor structure includes forming a plurality of first fin structures in a core region of a substrate and a plurality of second fin structures in a peripheral region of the substrate, forming a first dummy gate structure including a first dummy gate oxide layer and a first dummy gate electrode layer on each first fin structure and a second dummy gate structure including a second gate oxide layer and a second dummy gate electrode layer on each second fin structure. The method further includes removing each first dummy gate electrode layer, performing an ion implantation process to tune the threshold voltages of the first fin structures, and removing each first dummy gate oxide layer. The method also includes removing each second dummy gate electrode layer, and forming a gate dielectric layer and a metal layer on each first fin structure and each second fin structure.