Simple analytic procedures are given for finding the Fermi energy in a semiconductor with a parabolic or nonparabolic band structure, and (Al,Ga)As is treated as an example of a nonparabolic material in which each of the three conduction bands, &Ggr;,L, andX, competes effectively for electrons. The electron and hole Fermi energies form the basis for determining the voltage and further electrical characteristics of a semiconductor device.