In this work a semi analytical finite element formulation using Non-Uniform Rational B-Splines (NURBS) basis function is presented for modeling the dispersed wave propagation in heterogeneous waveguides. Convergence studies are carried out by considering a 2D constant-thickness isotropic elastic plate. The results were compared with the ones obtained by analytical methods and by conventional SAFE method. For all of cases, the dispersion curves evaluated by using enriched-NURBS basis have a significant better precision than using conventional Lagrangian elements (for the same number of degrees of freedom).