A semiconductor device, a semiconductor system, and a control method of a semiconductor device are capable of accurately monitoring the lowest operating voltage of a circuit to be monitored. According to one embodiment, a monitor unit of a semiconductor system includes a voltage monitor that is driven by a second power supply voltage different from a first power supply voltage supplied to an internal circuit that is a circuit to be monitored and monitors the first power supply voltage, and a delay monitor that is driven by the first power supply voltage and monitors the signal propagation period of time of a critical path in the internal circuit.