Disclosed are semiconductor packages and their fabrication methods. The semiconductor package comprises a lower semiconductor chip on a first redistribution substrate and including a through via, a lower molding layer on the first redistribution substrate and surrounding the lower semiconductor chip, a lower post on the first redistribution substrate and laterally spaced apart from the lower semiconductor chip, an upper semiconductor chip on the lower semiconductor chip and coupled to the through via, an upper molding layer on the lower molding layer and surrounding the upper semiconductor chip, an upper post on the lower molding layer and laterally spaced apart from the upper semiconductor chip, and a second redistribution substrate on the upper molding layer and coupled to the upper post. A top surface of the lower molding layer is at a level higher than that of a top surface of the lower semiconductor chip.