  We consider the electronic transport in bounded semiconductors in the
presence of an external magnetic field. Taking into account appropriate
boundary conditions for the current density at the contacts, a change in the
magnetoresistance of bulk semiconductors is found as compared with the usual
theory of galvanomagnetic effects in boundless media. New mechanism in
magnetoresistance connected with the boundary conditions arises. In particular,
even when the relaxation time is independent of the electron energy,
magnetoresistance is not vanish.
