A wafer level semiconductor package with a build-up layer is provided, which includes a glass frame having a through hole for receiving a semiconductor chip therein, a low-modulus buffer material filled within the space formed between the semiconductor chip and the glass frame, a build-up layer formed on the glass frame and the semiconductor chip such that the build-up layer is electrically connected to the semiconductor chip, and a plurality of conductive elements mounted on the build-up layer so that the semiconductor chip is electrically connected to external devices. With the use of the glass frame and low-modulus buffer material, the wafer level semiconductor package thus-obtained is free from warpage, chip-crack, and delamination problems and the reliability thereof is enhanced. A method for fabricating the wafer level semiconductor package is also provided.