A semiconductor device includes: a substrate having a first semiconductor layer, an insulating layer, and a second semiconductor layer; an active device on the substrate; an interlayer dielectric (ILD) layer on the active device; a first contact plug in the ILD layer and electrically connected to the active device; and a second contact plug in the ILD layer and the insulating layer, wherein a top surface of the second contact plug is higher than a top surface of the ILD layer.