A circuit modeling system includes a store a first net list. The first net list includes a plurality of semiconductor devices, a first power distribution network (PDN) connected to the plurality of semiconductor devices, and a signal network connected to the plurality of semiconductor devices that transmits signals to the plurality of semiconductor devices. A circuit simulation unit is configured to identify first semiconductor devices and second semiconductor devices from among the plurality of semiconductor devices. The first semiconductor devices are activated by receiving a signal through the signal network, and the second semiconductor devices are inactive. The circuit simulation unit is configured to reduce the first PDN to a second PDN based on the identified first semiconductor devices, and to generate a second net list including the signal network, the second PDN, and the first semiconductor devices.