In an embodiment, a device controls an internal power voltage in a semiconductor device. The device uses internal and external power voltages during a power-up period, and includes a power-up flag signal generator and a control circuit. The power-up flag signal generator generates a power-up flag signal based on the external power voltage. The control circuit provides a first internal power voltage to a peripheral circuit of the semiconductor device. During power-up the first internal power voltage varies according to a level of the external power voltage in response to the power-up flag signal having a first logic level. Accordingly, an internal power voltage may have a linear power-up slope during the power-up period and an initialization failure of any latch circuits in the peripheral circuit may be avoided. Also, power consumption of the latch circuits is reduced.