Level shifters capable of setting logic level of the output signals thereof to a pre-defined known state during power-up are provided, in which a first logic unit is powered by a first power voltage, receives input signals with a core power voltage and comprises first and second output terminals. First and second drivers are coupled between the first output terminal and the first power voltage and between the second output terminal and the second power voltage respectively. When one of the first and second power voltages is not ready during power-up, the first driver matches a voltage level on the first output terminal with the first power voltage by AC coupling and the second driver pulls low or maintains a voltage level on the second output terminal.