A 3D semiconductor device includes a conductive plate defining four sides and four recesses formed in the four sides, respectively. The conductive plate has first and second surfaces opposite to each other. A plurality of conductive leads are located in the recesses, respectively, and the conductive leads have first and second surfaces opposite to each other. A semiconductor die is attached onto the central area of the conductive plate. A plurality of conductive wires electrically connects the semiconductor die to the conductive leads. An encapsulant encloses, as in a capsule, the conductive plate, the conductive leads, the semiconductor die, and the conductive wires in such a manner that the first and second surfaces of the conductive plate and the first and second surfaces of the conductive leads are exposed to the outside.