  We study theoretically the two-dimensional topological electric state in a
single band semiconductor with strong spin-orbit interactions under harmonic
scalar electrostatic potentials. The electronic states described by the spin
Landau levels are insulating in the bulk and host gapless edge states in the
presence of time-reversal symmetry. Such topological states show the properties
of the quantized electric conductivity and the quantized spin Hall conductivity
characterized by the spin Chern number $\mathbb{Z}$. The quantization of the
two conductivities are robust under various perturbations such as the potential
disorder, the Zeeman field, and the spin-orbit scatterings. Existing
semiconductor technologies would realize the topological states discussed in
the present paper.
