Disclosed are a semiconductor package and semiconductor system in package using the same. The semiconductor package includes: a printed circuit board (PCB); a semiconductor die disposed on the PCB and having conductive posts formed on an upper surface of the semiconductor die; and a molding formed on the PCB to cover the semiconductor die, wherein the conductive posts have a surface exposed out of an upper surface of the molding. The semiconductor system in package includes: a first semiconductor package having a semiconductor die on which conductive posts are formed, and a molding formed so that upper surfaces of the conductive posts are exposed; and a second semiconductor package disposed on the first semiconductor package and electrically connected to the conductive posts.