Provided are a semiconductor device including a source/drain and a gate formed using a doped polysilicon process, and a method of fabricating the semiconductor device. The method comprises: forming a gate insulating layer on a part of an active region on a first conductivity type epitaxial layer; forming a conductive layer on the epitaxial layer; implanting high concentration impurities of a second conductivity type a first portion of the conductive layer on the gate insulating layer and second portions of the conductive layer on both sides of the first insulating layer; patterning the conductive layer; forming a second insulating layer on the epitaxial layer and high concentration impurity regions of the second conductivity type below the second conductive pattern; and implanting low-concentration impurities of the second conductivity type into the epitaxial layer between a gate structure and the high concentration impurity regions.