A method for fabricating semiconductor packages is proposed. A plurality of substrates each having a chip thereon are prepared. Each substrate has similar length and width to the predetermined length and width of the semiconductor package. A carrier having a plurality of openings is prepared. Each opening is larger in length and width than the substrate. The substrates are positioned in the corresponding openings, and gaps between the substrates and the carrier are sealed. A molding process is performed to form an encapsulant over each opening to encapsulate the chip. An area on the carrier covered by the encapsulant is larger in length and width than the opening. After performing a mold-releasing process, a plurality of the semiconductor packages are formed by a singulation process to cut along substantially edges of each substrate according to the predetermined size of the semiconductor package. A waste of substrate material is avoided.