A method of manufacturing a semiconductor package includes providing a semiconductor substrate including a plurality of first bottom connection pads, stacking a plurality of second semiconductor substrates on the semiconductor substrate, each of the second semiconductor substrates including a plurality of internal connection terminals, forming electrical connections between the internal connection terminals and the plurality of first bottom connection pads, disposing at least one adhesive sheet between adjacent ones of the semiconductor substrate and the plurality of second semiconductor substrates, applying heat and pressure to the plurality of second semiconductor substrates such that the adhesive sheet flows outwardly, forming a plurality of underfill fillets protruding outwardly, and forming a molding layer surrounding at least a portion of the plurality of second semiconductor substrates, all of the underfill fillets formed at different stacking levels are connected to each other to form a single continuous lateral underfill structure.