A dual polysilicon gate of a semiconductor device includes a substrate having a first region, a second region, and a third region, a channel region with a recessed structure formed in the first region of the substrate, a gate insulating layer formed over the substrate, a first polysilicon layer filled into the channel region, and formed over the gate insulating layer of the first and second regions, a second polysilicon layer formed over the gate insulating layer of the third region, and an insulating layer doped with an impurity, and disposed inside the first polysilicon layer in the channel region.