  In the present paper, we study the diffusion limit of the classical solution
to the unipolar Vlasov-Poisson-Boltzmann (VPB) system with initial data near a
global Maxwellian. We prove the convergence and establish the convergence rate
of the global strong solution to the unipolar VPB system towards the solution
to an incompressible Navier-Stokes-Poisson-Fourier system based on the spectral
analysis with precise estimation on the initial layer.
