Provided is a capacitor structure including a substrate, a cup-shaped lower electrode, a top supporting layer, a capacitor dielectric layer, and an upper electrode. The cup-shaped lower electrode is located on the substrate. The top supporting layer surrounds the upper portion of the cup-shaped lower electrode. The top supporting layer includes a high-k material. Surfaces of the cup-shaped lower electrode and the top supporting layer are covered by the capacitor dielectric layer. A surface of the capacitor dielectric layer is covered by the upper electrode.