The decay of the correlation function ( ) of an electron flow intensity near an instability point for the process of resonant tunneling through a double barrier structure is considered. It is supposed that the intensity of the incoming flow may fluctuate under the influence of an external noise, both white and colored. The correlation function ( ) behavior is analyzed, by using methods leading to the single-exponential approximation such as the method of projection operator and the method of mean relaxation time. Moreover, the method based on a combination of high-and low-frequency expansions of the Laplace transform of ( ), which has allowed the correlation function to be approximated by two decaying exponentials, is applied. The numerical simulation has shown that the latter approach unlike the others gives correct results near the instability point. K e y w o r d s: resonant tunneling, intensity correlation function decay, instability point.