There is a need to provide a semiconductor device, a semiconductor system, and a semiconductor device manufacturing method capable of accurately monitoring a minimum operating voltage for a monitoring-targeted circuit. A monitor portion of a semiconductor system according to one embodiment includes a voltage monitor and a delay monitor. The voltage monitor is driven by power-supply voltage SVCC different from power-supply voltage VDD supplied to an internal circuit as a monitoring-targeted circuit and monitors power-supply voltage VDD. The delay monitor is driven by power-supply voltage VDD and monitors signal propagation time for a critical path in the internal circuit. The delay monitor is configured so that a largest on-resistance of on-resistances for a plurality of transistors configuring the delay monitor is smaller than a largest on-resistance of on-resistances for a plurality of transistors configuring the internal circuit.