[en] The EM modes which occur at a 'surface quantized' plasma layer on a semiconductor surface have been calculated by a number of investigators using a model in which the plasma is represented by a two-dimensional (2-d) electron gas. Although the 2-d electron gas model is useful for many purposes, it cannot by its very nature take into account the interaction of the interface EM modes with the inter-subband excitations of the surface quantized levels, via the component of the electric field normal to the surface, within the finite-thickness plasma layer. In this approach the surface quantized plasma is represented by an anisotropic plasma slab having an effective thickness d* and a spatially uniform effective dielectric tensor. The model used here is a zeroth order approximation, in which all of the z dependent quantities, such as the charge density, the dielectric constants, etc., are replaced by their average values as spatially uniform parameters. (Auth.)