A MOS pass transistor includes a semiconductor layer having first conductivity, a trench isolation layer disposed in the semiconductor layer to define a first active region and a second active region, a first junction region having second conductivity, disposed in the first active region, and being in contact with a first sidewall of the trench isolation layer, a second junction region having the second conductivity, disposed in the second active region, being in contact with a second sidewall of the trench isolation layer, and being spaced apart from the first junction region, and a gate electrode disposed over the trench isolation layer. A lower portion of the gate electrode extends from a top surface of the trench isolation layer into the trench isolation layer to a predetermined depth.