  We discuss the Sakai-Sugimoto model at finite temperature and finite chemical
potential. It is a holographic model of large N_c QCD with N_f massless quarks
based on a D4/D8-\bar{D8} brane system. The near horizon limit of the D4-branes
and the probe approximation of the D8-\bar{D8} pairs allow us to treat the
D4-branes as a gravitational background and the D8-\bar{D8} pairs as a probe
which does not affect the background. We propose that the asymptotic value of a
U(1) gauge field on the D8-\bar{D8}-branes is identified with the chemical
potential for the baryon number. Using this chemical potential we analyze the
phase structure of this model and find a chiral symmetry phase transition of
the first order.
