A semiconductor device and methods thereof are disclosed. The proposed semiconductor device includes at least a unit cell wherein the unit cell includes a select transistor, and half of a ground-gate transistor electrically connected to the select transistor, and including a central conductive gate electrode region, two side conductive spacer regions and a gate dielectric layer, wherein a first and a second thicknesses of the gate dielectric layer underneath the two side conductive spacer regions are thinner than a third thickness of the gate dielectric layer underneath the central conductive gate electrode region.