FABRICATION METHOD OF DUAL GATE OXIDE

A method of fabricating a dual gate oxide of a semiconductor device includes forming a first gate insulation layer over an entire surface of a substrate, removing a portion of the first gate insulation layer to selectively expose a first region of the substrate using a first mask and performing an ion implantation on the selectively exposed first region of the substrate using the first mask, and forming a second gate insulation layer on the first gate insulation layer and the exposed first region of the substrate to form a resultant gate insulation layer having a first thickness over the first region of the substrate and a second thickness over a remaining region of the substrate, the first thickness and the second thickness being different.