An integrated circuit device as a first IC chip, a second IC chip, and a circuit board having a hole formed therein that is large enough to permit the second IC chip to be accommodated therein. The first and second IC chips are bonded together so as to be electrically connected together, and the first IC chip is mounted on the circuit board with the second IC chip accommodated in the hole formed in the circuit board. Here, one of the IC chips forming a chip-on-chip structure is accommodated in the hole formed in the circuit board, making further thickness reduction possible. Moreover, the obverse surfaces of the IC chips are located closer to the circuit board, making possible wireless mounting of the IC chips, despite forming a chip-on-chip structure, on the circuit board through connection using bumps. This helps reduce trouble due to inductance in a circuit that handles a high-frequency signal.