 Since the doping near the surface can also be controlled by electric fields, the work function of a semiconductor is also sensitive to the electric field in the vacuum.The reason for the dependence is that, typically, the vacuum level and the conduction band edge retain a fixed spacing independent of doping.This spacing is called the electron affinity (note that this has a different meaning than the electron affinity of chemistry); in silicon for example the electron affinity is 4.05 eV.