# Dependency of Conductivity on Temperature of Extrinsic Semiconductor

For an Extrinsic semiconductor ,how can we proof the following dependency of Conductivity on Temperature as shown in fig.:

My Thoughts:
At $0K$ there is no energy available , hence no electrons can flow from valence band to conduction band
$\therefore \sigma =0$ at $T=0K$
Now as $T$ increases ,energy increases and hence $\sigma$ increases
Now how $\sigma$ decreases as $T$ is further increased from $300K$ ?please help....