This paper presents an improved design approach for the self-oscillating command circuit, suitable for high self-sustained frequency, where the influence of the MOSFET gate-to-source capacitance is considered. The operation at high frequency presents the advantages as reduced size and weight for power electronics converters, for instance resonant converter. Furthermore, the use of the self-oscillating command circuit add low cost feature to the system. The self-oscillating resonant converter is designed by using the describing-function method and extended Nyquist stability criterion. Where, it allows the design of the system in a self-sustained operation point as well to predict more accurately the self-oscillating frequency.