A semiconductor device includes a PLL (Phase Locked Loop) circuit configured to generate a reception clock signal and a transmission clock signal based on a reference clock signal which has been subjected to frequency-modulation; a serializer configured to convert parallel data into serial data in response to the transmission clock signal to output the serial data; and a CDR (Clock Data Recovery) circuit configured to perform clock data recovery on reception data in response to the reception clock signal to output recovery data. A deserializer is configured to convert the recovery data into parallel data; and a loop-back line configured to supply the serial data outputted from the serializer to the CDR circuit as the reception data.