  We propose and show that the c-axis transport in high-temperature
superconductors is controlled by the pseudogap energy and the c-axis
resistivity satisfies a universal scaling law in the pseudogap phase. We
derived approximately a scaling function for the c-axis resistivity and found
that it fits well with the experimental data of
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$,
and YBa$_2$Cu$_3$O$_{7-\delta}$. Our works reveals the physical origin of the
semiconductor-like behavior of the c-axis resistivity and suggests that the
c-axis hopping is predominantly coherent.
