A semiconductor device includes a data bus, a data memory, a selector, a processor, and a debug controller. The selector is configured to be controlled by the debug controller to be in either a first selecting state in which the processor transmits a first signal to the data bus and a second selecting state in which the debug controller transmits a second signal to the data bus. The debug controller is configured to control the state of the selector based on the reception state of a predetermined command from an external device as well as the states of a read enable signal and a write enable signal from the processor such that, when the selector is in the second selecting state, the debug controller accesses the data bus via the selector.