  In realistic technicolor models containing many fermions, the electroweak
baryogenesis offers a natural scenario for generating baryon number asymmetry.
One of the key ingredients is the occurrence of the first order phase
transition at finite temperature. As a first step toward the exploration of
this possibility on the lattice, we develop an agile method to identify the
critical mass for a given Nf, separating the first order and the crossover
transition. We explain the outline of our method and demonstrate it by
determining the critical mass of Nf-flavors in the presence of light
two-flavors. It is found that the critical mass becomes larger with Nf.
