The slow relaxation kinetics on heterogeneous semiconductor surface are considered. Surface non‐homogeneity is taken into account using Gaussian and uniform distribution functions of the potential barriers, separating slow surface states from the semiconductor volume, in height g(W) or thickness g(d). The physical sense of the empirical parameters characterizing slow relaxation process is ascertained. The methods of definition of the distribution functions g(W) or g(d) through the experimental relaxation kinetics are discussed.