To achieve an accurate transfer of control from a system to a driver, a semiconductor device includes: a recognition unit that recognizes an object present in the periphery of a vehicle based on a result of observation of the periphery of the vehicle; a route calculation unit that calculates, based on the recognized object, a travel route for the vehicle in an automatic control mode for automatically controlling the vehicle; and a mode control unit that transfers the vehicle from the automatic control mode to a manual control mode for controlling the vehicle according to an operation by a driver, when a travel route to avoid the recognized object cannot be calculated.