First, we should understand how the carrier concentration varies with temperature in an intrinsic (pure) semiconductor.
At zero Kelvin (absolute zero), there are no free carriers in the semiconductor. In the 'bond model', this means that all the electrons are bound to the atom, as there is no energy available to break the bond. In the band-diagram, this is equivalent to the condition where all the electrons are residing in the valence band, no free electrons are in the conduction band.
As the temperature increases, the thermal energy increases, a few electrons attain enough energy to jump from the conduction band to the valence band (or to break free from the atom). As the temperature further increases, the thermal energy increases and the free carriers also increase (both electrons and holes, equally). This increase in intrinsic carrier concentration (\$n_i\$) is exponential in nature. (see image below). This increase in electron and hole concentrations happen even in doped semiconductors. (This is what is shown in the question).
Now consider the case when the semiconductor is doped with donor atoms. The dopant atoms contribute additional electrons to the semiconductor to make it n-type. Note that the doping concentration (\$N_D\$) will be so much higher than the intrinsic carrier concentration of the semiconductor, so that the intrinsic concentration is negligible (almost zero when plotted together) at room temperature. The electron concentration will thus be equal to the dopant concentration. \$n=N_D+n_i\approx N_D\$.
The dopant concentration is fixed. But the electron and hole concentration increases with temperature. Above some high temperature value, the value of hole concentration becomes significant and the increase will be visible as shown in the question. Note that both electron and hole concentrations are increasing and at very high temperatures, when the intrinsic carrier concentration becomes very much higher than that of the doping concentration, the semiconductor becomes intrinsic (it's no longer n-type). \$n=N_D+n_i\approx n_i\$, and \$p=n_i\$.
NB: This is one of the reasons why semiconductors have an upper limit on operating temperature.