A semiconductor device package includes a semiconductor chip and a plurality of inner leads, each having at least one slot formed along an upper surface of the inner lead. An adhesive layer is used to attach a bottom surface of the semiconductor chip to the upper surface of the inner lead. An encapsulant is allowed to flow in a package body mold, around the inner leads and through the slot. The slots prevent the production of turbulence along a side surface of the inner lead opposite to the flow direction, thereby avoiding problems associated with incomplete encapsulation such as the internal voids.