Glasses of GexAsxSe1-2x system were investigated during last ten years by the means of T-modulated differential-scanning calorimetric technique [1,2], by the Raman and neutron scattering methods [3], by the Mossbauer spectroscopy and the nuclear magnetic resonance [4]. This has allowed to determine the flexible (free from mechanical stress) at x<xc(1)=0.09, the intermediate - at xc(1)<x<xc(2)=0.16, and the stressedrigid - at x>xc(2) phases. Despite of accumulated results, some questions remain opened. First, the definition of an intermediate phase and a threshold of rigidity in amorphous films are not present clearly as the majority of the listed above methods cannot be applied in this case. Second, the effects of the examined phase transitions onto optical, photo-electric and transport properties of a material are poorly studied, however they are source of additional information about the film structure near these transitions. In the given work we have focused our attention on these problems, and the amorphous films of GexAsxSe1-2x were investigated in a wide range of compositions x, ranging from x=0.05 up to x=0.30 (see Fig.1), by a photocapacitance relaxation technique. The idea of use of the capacitance relaxation technique in our studies is based on the fact that the low-frequency permittivity of a chalcogenide film is caused by electric dipoles, which are formed by pairs of defects with negative correlation energy (U-minus). Such dipoles can be induced by a light from the region of strong absorption [5], or excited by a heating of sample [6], and to serve not only as object of study, but also as intrinsic probe, which allows to test rigidity of network. In this (last) statement specific ability of defects with U-minus to reorganize the environment during polarization of a material is incorporated. It is directly associated with mechanical rigidity of glass-forming network. The more rigid is the network, the more hardly and slowly there is a turn of a dipole in a direction of the applied electric field, and vice versa, in the soft (flexible) environment polarization is faster. The capacitance current (or otherwise, a displacement current) was measured as the response to a triangular voltage pulses, which was applied to the sample: Idis.c.=kC(t), k=dV(t)/dt (frequency 2 x 10-2 Hz, amplitude ~ 0.2 V). Compositional dependencies of the low-frequency dielectric permeability, decay time constant and the Kohlrausch parameter of nonexponentiality are deduced from these data. All parameters show two compositional thresholds, one situated near the xc(1)=0.09, and another - near the xc(2)=0.16-0.18.imageFig. 1. The diagram of the investigated compositions (x) on an axis of average coordination number <r>, in samples GexAsxSe1-2x. The arrow shows Phillips-Thorpe threshold. The thresholds xC(1) and xC(2), which were reported by some authors (see [1-4]), are shown by shaded regions.