A semiconductor device is composed of a first IC chip having a data processing function and a second IC chip having a non-volatile memory for storing confidential reference data. Both of the IC chips are provided with connection pads on the facing sides of the two chips, so that they can be bonded in a chip-on-chip configuration. Each of the connection pads of the second IC chip is located at the position of a corresponding connection pad of the first IC chip. An externally input data is compared with the reference data for verification. The input data is authenticated based on the result of the verification.