Graphical method to determine the Fermi level position of the free surface of a semiconductor with a uniform distribution of surface states. Plotted in same figure are the space charge of the semiconductor (for different doping levels: BLUE for n-type semiconductors and PINK for p-type semiconductors) and the negative of the net charge due to the surface states (RED). Where a curve intersects the red straight line is the position of the surface Fermi level position for that particular semiconductor doping level.