In a semiconductor device for power management and a semiconductor system including the same, the semiconductor device includes an open loop source generator configured to generate an open loop source, an interface configured to output a dynamic voltage source (DVS) code based on the open loop source, a monitoring unit configured to receive a power supply voltage generated based on the DVS code as a feedback and generate a monitoring signal, and a phase difference measurement unit configured to compare the open loop source with the monitoring signal and set a hold time corresponding to an arithmetic period in a closed loop.