A method for designing a semiconductor device having a plurality of logic elements provided with a plurality of power supplies. First, a power supply type name is given to each power supply in accordance with the purpose of the power supply in each logic element. Each logic element is associated with the power supply type name of the power supply that is to be provided to the logic element. A power supply group is formed for each power supply. Specific information of each power supply group associating the power supply type name with supplied voltage is generated. Then, the power supply provided to each logic element is determined by allocating the power supply group to the logic element. The method simplifies designing the layout of a semiconductor device operated by multiple power supplies.