A semiconductor package includes a substrate having a first surface and a second surface opposing the first surface; a plurality of first pads disposed on the first surface of the substrate and a plurality of second pads disposed on the second surface of the substrate and electrically connected to the plurality of first pads; a semiconductor chip disposed on the first surface of the substrate and connected to the plurality of first pads; a dummy chip having a side surface facing one side surface of the semiconductor chip, disposed on the first surface of the substrate spaced apart from the semiconductor chip in a direction parallel to the first surface of the substrate, the dummy chip having an upper surface positioned lower than an upper surface of the semiconductor chip in a direction perpendicular to the first surface of the substrate; an underfill disposed between the semiconductor chip and the first surface of the substrate, and having an extension portion extended along the facing side surfaces of the semiconductor chip and the dummy chip in the direction perpendicular to the first surface of the substrate, an upper end of the extension portion being disposed to be lower than the upper surface of the semiconductor chip; and a sealing material disposed on the first surface of the substrate, and sealing the semiconductor chip and the dummy chip.