摘要： Aims. The electron plasma frequency ωpe and electron gyrofrequency Ωe are two parameters that allow us to describe the properties of a plasma and to constrain the physical phenomena at play, for instance, whether a maser instability develops. In this paper, we aim to show that the maser instability can exist in the solar corona. Methods. We perform an in-depth analysis of the ωpe/Ωe ratio for simple theoretical and complex solar magnetic ?eld con?gurations. Using the combination of force-free models for the magnetic ?eld and hydrostatic models for the plasma properties, we determine the ratio of the plasma frequency to the gyrofrequency for electrons. For the sake of comparison, we compute the ratio for bipolar magnetic ?elds containing a twisted ?ux bundle, and for four di?erent observed active regions. We also study how ωpe/Ωe is a?ected by the potential and non-linear force-free ?eld models. Results. We demonstrate that the ratio of the plasma frequency to the gyrofrequency for electrons can be estimated by this novel method combining magnetic ?eld extrapolation techniques and hydrodynamic models. Even if statistically not signi?cant, values of ωpe/Ωe ≤ 1 are present in all examples, and are located in the low corona near to photosphere below one pressure scale-height and/or in the vicinity of twisted ?ux bundles. The values of ωpe/Ωe are lower for non-linear force-free ?elds than potential ?elds, thus increasing the possibility of maser instability in the corona. Conclusions. From this new approach for estimating ωpe/Ωe, we conclude that the electron maser instability can exist in the solar corona above active regions. The importance of the maser instability in coronal active regions depends on the complexity and topology of the magnetic ?eld con?gurations.