A semiconductor device includes a first conductive structure extending along a vertical direction and a second conductive structure extending along the vertical direction. The second conductive structure is spaced apart from the first conductive structure along a first lateral direction. The semiconductor device includes third conductive structures each extending along the first lateral direction. The third conductive structures are disposed across the first and second conductive structures. The semiconductor device includes a first semiconductor channel extending along the vertical direction. The first semiconductor channel is disposed between the third conductive structures and the first conductive structure, and between the third conductive structures and the second conductive structure. The first and second conductive structures each have a first varying width along the first lateral direction, and the first semiconductor channel has a second varying width along a second lateral direction.