Abstract: Starting from the current-voltage equation given by A. Van der Ziel (1976), a dif-ferential equation of the normalized fluctuation is developed. Expanding the Pourier transform of the fluctuation into a power series in the parameter j and solving the equation developed, we get all order analytical solutions of the Fourier transform of the fluctuation in drain and gate. The spectral desities of noise current of drain and gate as well as the correlation coefficient are also obtained. The effect of the higher order solutions of the equation on the noise spectra is shown in the conclusion.