A fabrication method of a chip scale package includes: disposing a chip on a carrier board and embedding the chip into a composite board having a hard layer and a soft layer; and removing the carrier board so as to perform a redistribution layer (RDL) process, thereby solving the conventional problems caused by directly attaching the chip on an adhesive film, such as film-softening caused by heat, encapsulant overflow, chip deviation and contamination, etc., all of which may result in poor electrical connection between the wiring layer and the chip electrode pads in the subsequent RDL process and even waste products as a result.