A semiconductor device includes a semiconductor structure, a first dielectric layer and a plurality of multilayer stacks. The semiconductor structure includes conductive features therein. The first dielectric layer is on the semiconductor structure. The multilayer stacks are arranged on the first dielectric layer. Each of the multilayer stacks comprises a semiconductor layer over the first dielectric layer, a conductive layer over the semiconductor layer and a second dielectric layer over the conductive layer. The second dielectric layer includes a top portion and a bottom portion wider than the top portion.