A semiconductor apparatus includes first and second address buffer groups. The first address buffer group receives first address signals from an external source and outputs the first address signals to a first internal circuit, in first and second operation modes. The second address buffer group receives second address signals from the external source and outputs the second address signals to the first internal circuit, in the first operation mode, and receives third address signals which are generated in a second internal circuit and outputs the third address signals to the first internal circuit, in the second operation mode.