A correlation between the recombination rate constant of free electrons and holes (k r ) and the band gap (E g ) of semiconductors (AgCl, AgBr, Cd x Zn 1-x S, CdSe, CdTe, and their solid solutions) at 295 K was found. The experimental data were obtained by the UHF photocon ductivity (36 GHz) using current carrier generation by laser pulses (λ = 337 nm, pulse duration 8 ns). A decrease in E g in a range of 1.5-3 eV increases k r by 1.5 orders of magnitude according to the law close to exponential.Two key processes, namely, separation and recombi nation, determine changes in the charged particles gener ated in the matter by the light or ionizing radiation. The most part of technical applications using compounds of the A II B VI and A I B VII types are based on the process of charge separation, whose characteristics determine the sensitivity and time parameters of various devices, e.g., solar energy converters, sensors for radiation detection, systems of information transfer and recording, and others. In these substances electron hole recombination processes most frequently result in irretrievable energy losses, ex cept for some types of recombination luminescence. How ever, quantitative data on the characteristics of this pro cess are virtually lacking, although their absence notice ably retards progress in the area of application of these compounds, impeding prediction of the limiting charac teristics of the developed devices.Note that quantitative regularities of recombination of free (that have never been captured by traps) electrons and holes in semiconductors of other types are not quite clear, despite the fact that the problem on the relationship of the recombination rate constant (k r ) and the properties of semiconductors were discussed in a series of publica tions. For instance, on the basis of the estimates for the k r values in the Ge and Si semiconductors (∼5•10 -14 and ∼3•10 -15 cm 3 s -1 , respectively), which were obtained us ing the dependence of the absorption coefficient on the band gap (E g ) and the principle of detailed balancing, it was assumed that the rate constant should increase with a decrease in E g . Although it should additionally be sub stantiated that the principle of detailed balancing can be applied to an electron that underwent the thermalization step after its generation, this concept met no basic objec tions so far.Meanwhile, in the recent decade there were several attempts to experimentally determine the rate constants k r /cm 3 s -1 (cross sections) of electron hole recombina tion in compounds of the A II B VI and A I B VII types: 1•10 -11 (AgBr (powders), E g = 2.6 eV, 2 2•10 -12 (AgCl (powders), E g = 3.1 eV; 3 (3±1)•10 -13 (CdS, E g = 2.5 eV) 4 ; (3±1)•10 -11 (CdTe, E g = 1.6 eV) 5 ; (4-6)•10 -11 (CdSe, E g = 1.8 eV). 6 However, no relationship was revealed between the obtained constants and the properties of sub stances.In the present work, we attempted to verify some ear lier published data on the rate constants of electron hole recombination in compounds of the A II B VI...