An interposer includes a base layer including a first surface and a second surface that are opposite to each other. An interconnect structure is disposed on the first surface. The interconnect structure includes a metal interconnect pattern and an insulating layer surrounding the metal interconnect pattern. A first lower protection layer is disposed on the second surface. A plurality of lower conductive pads is disposed on the first lower protection layer. A plurality of through electrodes penetrates the base layer and the first lower protection layer. The plurality of through electrodes electrically connects the metal interconnect pattern of the interconnect structure to the lower conductive pads. At least one of the insulating layer and the first lower protection layer has compressive stress. A thickness of the first lower protection layer is in a range of about 13% to about 30% of a thickness of the insulating layer.