A semiconductor system includes a controller and a semiconductor device that may communicate signals with the controller through a single input/output pad. The semiconductor device includes a self power generation block that may generate a driving voltage in response to a first signal inputted from the controller through the single input/output pad, and generate a start-up signal when the driving voltage is over a set voltage, a state machine block that may detect a pulse width of a second signal inputted from the controller through the single input/output pad, in response to the start-up signal, and may generate commands and data in response to the pulse width, and a data output block that may convert the data into a third signal of a current level corresponding to the data and output the third signal to the controller through the single input/output pad, in response to the commands.