  By considering the effect of diffusion on the external electric field
response of charge carriers in metals and semiconductors, it is shown that the
finite temperature correction proposed Bostrom and Sernelius requires
substantial modification, and there is no large correction as suggested for
good conductors. The apparent violation of the Third Law of Thermodynamics of
the various proposed temperature corrections to the Casimir force is also
resolved. Finally, the effect of Debye screening on electrostatic calibrations
between pure germanium surfaces is calculated
