A new robust high order sliding mode controller for a class of uncertain minimum-phase single input-single output (SISO) nonlinear systems is designed. The high order sliding mode problem is formulated in input-output term and is viewed in uncertain linear context by considering uncertain nonlinear functions as bounded non structured parametric uncertainties. A sliding manifold is designed in order to ensure finite-time convergence of sliding variable high order time derivatives. The control law allows the establishment of an $r^{th}$ order sliding mode. This result is extended to multi input-multi output (MIMO) systems.