The mechanisms of forming a semiconductor device package described above provide a low-cost manufacturing process due to the relative simple process flow. By forming an interconnecting structure with a redistribution layer(s) to enable bonding of one or more dies underneath a package structure, the warpage of the overall package is greatly reduced. In addition, interconnecting structure is formed without using a molding compound, which reduces particle contamination. The reduction of warpage and particle contamination improves yield. Further, the semiconductor device package formed has low form factor with one or more dies fit underneath a space between a package structure and an interconnecting structure.