The distribution of potential in the space charge region of a semiconductor results in a change in the electron energy levels with distance from the interface. This is usually described as 'bending of the energy bands'. Thus the bands are bent, upwards if \(\sigma >0\) and downwards if \(\sigma <0\), where \(\sigma \) is the free charge density. When \(\sigma =0\) the condition of flat bands is met, provided no surface states are present.