A method for automatic operating voltage detection, in which one internal supply voltage (vdd) is selected from at least two different external supply voltages, with a first external voltage supply (VDDA) being applied permanently, is based on the object of reducing the circuit complexity for automatic operating voltage detection, the operating current caused by the selection arrangement and the required chip area, in which case the voltage ratios between the two different external supply voltages can be as required. This object is achieved in that a reference voltage (Vref) and a voltage (VDDreg) is produced from the first external supply voltage (VDDA), the reference voltage (Vref) is compared with a second external supply voltage (VDDIO), and either the voltage (VDDreg) produced from the first external supply voltage (VDDA) or the second external supply voltage (VDDIO) is released as an internal supply voltage (vdd), depending on the comparison.