  We discuss interstellar temperature determinations using the excitation
equilibrium of the ^2P levels of Si II and C II. We show how observations of
the ^2P_3/2 fine structure levels of Si II and C II (which have significantly
different excitation energies, corresponding to ~413 and 92 K, respectively)
can be used to limit gas kinetic temperatures. We apply this method to the
z=4.224 damped Lyman-alpha system toward the quasar PSS1443+27. The lack of
significant absorption out of the SiII ^2P_3/2 level and the presence of very
strong C II ^2P_3/2 provides an upper limit to the temperature of the C
II*-bearing gas in this system. Assuming a solar Si/C ratio, the observations
imply a 2-sigma limit T<954 K for this absorber; a super-solar Si/C ratio gives
stricter limits, T<524 K. The observations suggest the presence of a cold
neutral medium; such cold gas may serve as the fuel for star formation in this
young galaxy.
