Chalcogenide viti·eous semiconductors of the As-S-Se system exhibit photostiuctural ti·ansfo1mations with reversible and iITeversible prope1iies, and are promising materials as registration media for holography and optical infonnation, for fabrication of diffractive elements, and other optoelecti·onic applications [1]. Because many optoelecti·onic devices on ammphous semiconductors are based on the photoconductivity effect, special interests represent investigation of the stationary and non-stationary characteristics of photoconductivity [2]. The photoconductivity specti·a can give the infonnation regarding the processes of generation, drift and recombination of non-equilibrium cunent can-iers. Fig. I represents the specti·al distribution of photocunent for amo1phous (As4S3Se3)0_97:Sno.03 thin films at positive ( curve 1) and negative ( curve 2) polarities at the top illuminated electi·ode. For other (As4S3Se3)1-x:Snx (0<=x<=10 at. %Sn), the shape of the curves of the specti·al distribution of photocunent is siinilar. fu all cases the photocunent at positive polarity at the top illuminated electi·ode is higher and the maximum of the specti·al disu-ibution is shifted in the high energy region of the spectrum (Fig.2). The well known method by Moss rnle for dete1mining the forbidden band gap Eg from the photoconductivity spectra of the semiconductor is the long wavelength Ao at which the photosensitivity reach a half value of the maxiinum, as is shown in Fig. I. The dependence of the calculated values of Eg versus Sn concentration in amo1phous (As4S3Se3)i-x:Snx thin films has a minimum at around 6.0 at. %Sn, which probably is connected with fo1mation of new tetrahedral units SnSe2.The photosensitivity of amo1phous (As4S3Se3)1-x:Snx thin films decrease when Sn is inti·oduced in the host glass, and is almost constant for all Sn-containing glasses. fu Fig.3 are shown the nonnalized cmves of the specu-al disu-ibution of photocmTent log(Ip,/No)=f(h 0 for amo1phous As4S3Se3 thin films. The same dependences exhibit all amo1phous (As4S3Se3)1-x:Snx thin films of different investigated compositions.