Abstract Plasma resonance line has been observed in n-type InSb at helium temperatures, as a function of pulsed electric field. An increasing electric field shifts the resonance line in the direction of lower magnetic field. This is accounted for, qualitatively, by increase in the effective mass of the “heated” electrons. “Hot” plasma can be observed only when impurity scattering dominates the relaxation processes. The shifts increase when the plasma frequency approaches the operating frequency.