Upon doping an intrinsic semiconductor with an impurity, its...

The conductivity of a semiconductor is given by $\sigma = e(n_e \mu_e + n_h \mu_h)$, where $n_e$ and $n_h$ are the number densities of electrons and holes respectively.

When an intrinsic semiconductor is doped with an impurity (either trivalent or pentavalent), the number of majority charge carriers (either holes or electrons) increases drastically.

This increase in the concentration of charge carriers results in a significant increase in the electrical conductivity of the semiconductor.

Thus, upon doping an intrinsic semiconductor with an impurity, its conductivity increases.