The reduction of chatter in variable structure control (VSC) systems is considered. In this scheme the time derivative of the control law is discontinuous on a suitable manifold of an augmented order state space. For the case of differential equations with uncertain RHS, the proposed scheme maintains the robustness properties of classical VSC if an estimator of inaccessible state components is introduced. A separation property, together with the convergence of the proposed estimator are proved. Some simulation results relating to an induction motor control problem are finally presented.