The coupling of energy among electron‐acoustic, ion‐acoustic, and transverse electromagnetic waves at a density discontinuity in a two‐fluid fully ionized plasma is studied by means of the plane wave solutions of the linearized equations of hydrodynamics and Maxwell's equations. An expression for energy conservation in a two‐fluid plasma is discussed and applied to energy coupling among the three allowed modes. Numerical results for all types of wave coupling illustrate the influence of the plasma parameters on the efficiency of energy conversion.