  Interface states at a boundary between regions with different spin-orbit
interactions (SOIs) in two-dimensional (2D) electron systems are investigated
within the one-band effective mass method with generalized boundary conditions
for envelope functions. We have found that the interface states unexpectedly
exist even if the effective interface potential equals zero. Depending on the
system parameters, the energy of these states can lie in either or both
forbidden and conduction bands of bulk states. The interface states have chiral
spin texture similar to that of the edge states in 2D topological insulators.
However, their energy spectrum is more sensitive to the interfacial potential,
the largest effect being produced by the spin-dependent component of the
interfacial potential. We have also studied the size quantization of the
interface states in a strip of 2D electron gas with SOI and found an unusual
(non-monotonic) dependence of the quantization energy on the strip width.
