An interposer includes a first redistribution layer, an organic substrate, a capacitor, a hard mask layer, a conductive pillar, and a second redistribution layer. The organic substrate is on the first redistribution layer. The capacitor is embedded in the organic substrate and includes a first electrode layer, a second electrode layer, and a capacitor dielectric layer between the first electrode layer and the second electrode layer. The first electrode layer electrically connects with the first redistribution layer. The hard mask layer is on the organic substrate. The conductive pillar is embedded in the organic substrate and the hard mask layer and electrically connects with the first redistribution layer. The second redistribution layer is on the hard mask layer and electrically connects with the second electrode layer and the conductive pillar.