  In this paper, the semiclassical limit of Davey-Stewartson systems are
studied. It shows that these dispersionless limited integrable systems of
hydrodynamic type, which are defined as dDS (dispersionless Davey-Stewartson)
systems, are arisen from the commutation condition of Lax pairs of
one-parameter vector fields. The relevant nonlinear Riemann-Hilbert problems
with some symmetries for the dDS-II system are also constructed. This kind of
Riemann-Hilbert problems are meaningful for applying the formal inverse
scattering transform method, recently developed by Manakov and Santini, to
study the dDS-II system .
