  We show that the spin-orbit interaction induced by the boundary confining
potential causes opposite spin accumulations on the transverse edges in a zonal
two-dimensional electron gas in the presence of external longitudinal electric
field. While the bias is reversed, the spin polarized direction is also
reversed. The intensity of the spin accumulation is proportional to the bias
voltage. In contrast to the bulk extrinsic and intrinsic spin Hall effects, the
spin accumulation by the confining potential is almost unaffected by impurity
and survives even in strong disorder. The result provides a new mechanism to
explain the recent experimental data.
