Serial communication with a bit rate close to a required bit rate can be performed, regardless of the frequency of an operation clock.A semiconductor device includes a serial communication interface that operates according to a certain operation clock. The serial communication interface is provided with a baud rate generator that generates a basic clock for counting the operation clock to define the unit transfer time based on the count, and a transmission/reception controller for performing control of transmission and reception according to the generated basic clock. Further, the serial communication interface is provided with a bit rate modulator capable of realizing a desired bit rate by partially masking supply of the operation clock to the baud rate generator, and thereby serial communication with a bit rate close to a required bit rate is realized.