  The purpose of this paper is to study radial solutions for steady
hydrodynamic model of semiconductors represented by Euler-Poisson equations
with sonic boundary. The existence and uniqueness of radial subsonic solution,
and the existence of radial supersonic solutions are derived by using the
energy method and the compactness method, but under a general condition of the
doping profile. In particular, for radial supersonic solutions, it is more
difficult to get the related estimates by the effect of high dimensional space
and the sonic boundary, so we apply a special iteration to complete the proofs.
The results obtained essentially improve and develop the previous studies in
the one-dimensional case.
