This paper discusses an instability of extraordinary Bernstein waves, driven by a beam of energetic electrons. The present research is motivated by the study of solar radio emission processes, and its findings may have interesting implications. Specifically, the extraordinary Bernstein waves excited both below and above the plasma frequency by the present instability can, in principle, mode convert to either of the free-space propagating modes in the presence of magnetic field and/or density inhomogeneities. This paper is devoted to an analysis of the basic properties associated with the present instability over a wide range of various physical parameters. ¿ 1999 American Geophysical Union