A circuit board structure and a fabrication method thereof are disclosed. The circuit board structure includes a carrying board having a first and an opposite second surface and having at least one through cavity formed therein; a semiconductor chip disposed in the through cavity of the carrying board; an adhesive material filling the gap between the through cavity of the carrying board and the semiconductor chip to fix the semiconductor chip in the through cavity; and a reinforcing layer disposed on the second surface of the carrying board and the inactive surface of the semiconductor chip, thereby increasing the strength of the carrying board as well as the reliability of the circuit board.