A improved method of the microwave diagnostics for the determination of the electron density in the column plasma of de glow discharges is presented. This method overcomes significant limitations involved in the conventional method. The latter is mainly based on the measurement of the resonance frequency shift of the resonator cavity caused by the presence of the de column plasma and is strictly valid only in the so-called high field frequency limit of the resonator operation. Of significant importance with respect to the improved method is the additional inclusion of the measurable phase delay between the electric hf field, superimposed on the dc plasma by the microwave field of the resonator, and the induced hf electron current. This new method has been critically evaluated with respect to its extended applicability and has been successfully applied to the experimental determination of the electron density in dc plasmas of neon and molecular nitrogen.