A method for controlling voltage of a doped well in a substrate is provided. The substrate and the doped well are in different conductive type. The method includes applying a substrate voltage to the substrate while a well power for applying a well voltage to the doped well is turned off. The method also includes detecting a voltage level of one of the doped well and the substrate to judge whether or not a voltage target is reached. The well power is turned on to apply the well voltage to the doped well when the voltage level as detected reaches to the voltage target.