  We consider the effect of reionization on the clustering properties of galaxy
samples at intermediate redshifts (z~0.3-5.5). Current models for the
reionization of intergalactic hydrogen predict that overdense regions will be
reionized early, thus delaying the build up of stellar mass in the progenitors
of massive lower-redshift galaxies. As a result, the stellar populations
observed in intermediate redshift galaxies are somewhat younger and hence
brighter in overdense regions of the Universe. Galaxy surveys would therefore
be sensitive to galaxies with a somewhat lower dark matter mass in overdense
regions. The corresponding increase in the observed number density of galaxies
can be parameterized as a galaxy bias due to reionization. We model this
process using merger trees combined with a stellar synthesis code. Our model
demonstrates that reionization has a significant effect on the clustering
properties of galaxy samples that are selected based on their star-formation
properties. The bias correction in Lyman-break galaxies (including those in
proposed baryonic oscillation surveys at z<1) is at the level of 10-20% for a
halo mass of 10^12 solar masses, leading to corrections factors of 1.5-2 in the
halo mass inferred from measurements of clustering length. The reionization of
helium could also lead to a sharp increase in the amplitude of the galaxy
correlation function at z~3. We find that the reionization bias is
approximately independent of scale and halo mass. However since the traditional
galaxy bias is mass dependent, the reionization bias becomes relatively more
important for lower mass systems. The correction to the bias due to
reionization is very small in surveys of luminous red galaxies at z<1.
