A semiconductor device includes a first dielectric layer on a substrate, a hard mask layer on the first dielectric layer, a trench in the hard mask layer and the first dielectric layer, a first source/drain electrode layer on a sidewall of the trench, a second dielectric layer on the first source/drain electrode layer in the trench, a second source/drain electrode layer on the second dielectric layer in the trench, a third dielectric layer on the second source/drain electrode layer in the trench, a 2D material layer overlying the hard mask layer, the first source/drain electrode layer, the second dielectric layer, the second source/drain electrode layer, and the third dielectric layer, a gate dielectric layer on the 2D material layer, and a gate electrode on the gate dielectric layer.