To provide a semiconductor device and portable telephone equipment using the semiconductor device capable of mounting a D-class digital amplifier and achieving a high power efficiency.

In a first sampling frequency conversion circuit S1, sampling frequency conversion processing of a digital music signal SDM is performed. Addition or subtraction processing between the digital music signal SDM on which the sampling frequency conversion processing has been performed and a digital voice signal SDV2 is performed in a second digital processing circuit D2. Further, in a second sampling frequency conversion circuit S2, sampling frequency conversion processing of a digital voice signal SDV1 is performed. Also, addition or subtraction processing between the digital voice signal SDV1 on which the sampling frequency conversion processing has been performed, and the digital voice signal SDV2 is performed in a third digital processing circuit D3.