A semiconductor device includes a substrate including a first region and a second region adjacent to the first region, the first and the second regions being disposed in a first direction parallel to an upper surface of the substrate; an etch-stop layer disposed on the first region and the second region; a separation layer disposed on an upper portion of the etch-stop layer, the separation layer being disposed on the first region; a high-electron-mobility transistor (HEMT) element disposed on an upper portion of the separation layer in a second direction perpendicular to an upper surface of the substrate; a light-emitting element disposed on the second region between the substrate and the etch-stop layer; and a plurality of first insulating patterns covering side surfaces of the HEMT element, the plurality of first insulating patterns extending to the etch-stop layer.