A capacitor includes a solid conductive plate, a first electrode, and a second electrode. The solid conductive plate is disposed above a substrate of a wafer. The solid conductive plate serves as a bottom plate of the capacitor. The first electrode is disposed above the solid conductive plate so that the solid conductive plate is located between the substrate and the first electrode. This first electrode serves as a top plate of the capacitor. The second electrode is disposed above the solid conductive plate, and is disposed beside the first electrode. The second electrode is electrically connected to the solid conductive plate.