By using the lattice Monte-Carlo simulation, we investigate the finite temperature (T) chiral phase transition at color SU(3) gauge theories with various species of fundamental fermions, and discuss the signal of the (pre-)conformality at large Nf (num. of flavors.) via their comparisons. As Nf increases, we observe stronger fermion screening effects which result from a larger fermion multiplicity. We investigate a finite T step-scaling associated with a uniqueness of the critical temperature (Tc) at each Nf, then the vanishing step-scaling indicates the emergence of the conformality around Nf* = 10 - 12. Further, motivated by the functional renormalization group analyses, we examine the Nf dependence of Tc, whose vanishing behavior indicates the onset of conformal window around Nf* = 9 - 10.