In a transmission portion of a semiconductor device, a first amplification portion receives a digital baseband signal and amplifies the signal with a first gain through digital processing. A digital-to-analog conversion portion converts the digital baseband signal amplified by the first amplification portion into an analog baseband signal. A modulation portion generates a transmission signal by modulating a local oscillation signal with the analog baseband signal. A second amplification portion amplifies the transmission signal with a variable second gain. A control unit receives information representing a transmission mode and adjusts the first gain in accordance with the transmission mode.