A contact structure is provided, including a substrate, an active layer, an inter-layer dielectric (ILD) layer, a contact opening, and a conductive layer. The active layer is disposed over the substrate, and the insulating layer is disposed over the active layer; an inter-layer dielectric (ILD) layer over the insulating layer. The contact opening penetrates a portion of the ILD layer and the insulating layer to expose a portion of the active layer, wherein the contact opening includes a first recess portion, and the first recess portion is defined by a bottom surface of the ILD layer, a sidewall of the insulating layer and a top surface of the active layer. The conductive layer is in the contact opening and is electrically connected to the active layer.