A system to perform a reference voltage training operation may include: a controller configured to output a dock signal, a chip selection signal, a command address and data; and a semiconductor device configured to enter a training mode to control the level of a reference voltage when the chip selection signal and the command address are a first logic level combination in synchronization with the clock signal, configured to enter an ID setting mode to set a storage ID when the chip selection signal and the command address are a second logic level combination, and configured to enter an ID selection mode to update a voltage code that is generated in the training mode when the chip selection signal and the command address are a third logic level combination.