The experimental magnetic‐field derivative of the microwave absorption signal, obtained using electron paramagnetic resonance techniques, has a line shape that depends on the Ginzburg–Landau model parameter &kgr; of the superconducting sample at a given temperature. The type‐II superconducting equation of state can be utilized to describe the drop in the output microwave power derivative, from its maximum atH&bartil;Hc1to its much lower values whenH≫Hc1, in order to estimate the values of &kgr;. The technique also allows for the experimental determination of hysteretic behavior inBas a function ofH.