Surface plasmon waveguides show promise as sub-wavelength signal elements in integrated optoelectronic devices. Modulation of these signals requires designs that are compatible with existing semiconductor fabrication technologies, such as MOS structures. We show that waveguides of this type are not only practical, but offer distinct advantages. In particular, an asymmetric geometry is shown to support very long-range modes. In preliminary experimental results we report the observation of these modes in an visible wavelength analog structure. Our models predict that these characteristics can be maintained while shifting the operating conditions to the fiber communications band in waveguides constructed in silicon.