The characteristics of electromagnetic surface waves supported by a plane interface separating a semi‐infinite region of free space from another semi‐infinite region consisting of a background plasma permeated by a neutralized beam streaming parallel to the interface are investigated for the case in which the wave is progressing either in, or opposite to, the direction of the beam. As compared to the case of a stationary plasma, the surface wave has new branches and drastically different characteristics. For the case of waves progressing opposite to the direction of the beam, there are backward‐wave regions as well as regions of instability if the beam is sufficiently strong. These regions of instability occur below the plasma frequency. In general, there are two frequency ranges of instability in which the surface wave undergoes traveling wave amplification in the direction of the stream. The wave amplification characteristics are studied and their dependence on the number density of the beam relative to the background plasma is examined.