A method for fabricating a semiconductor device includes forming a sacrificial layer over a substrate, forming a contact hole in the sacrificial layer, forming a pillar to fill the contact hole. The pillar laterally extends up to a surface of the sacrificial layer and then the sacrificial layer is removed. The method further includes forming a gate dielectric layer over an exposed sidewall of the pillar, and forming a gate electrode over the gate dielectric layer. The gate electrode surrounds the sidewall of the pillar.