The total momentum and energy conservation relations between particle kinetic energy and wave energy is satisfied for the plasma–maser instability. The Manley–Rowe relation for plasma waves is violated and as a result an efficient energy up‐conversion from the low‐frequency mode to the high‐frequency mode is possible even for a normal unreversed electron population in plasma turbulence. The entropy production rate for plasma turbulence with plasma–maser instability is estimated. The plasma–maser instability always coexists with the quasilinear interaction, thus it has a potential importance to interpret numerous experiments in fusion and astrophysical plasmas.