The report presents the results of a theoretical investigation of the photovoltaic effect in thin variable-gap semiconductor layers whose thickness is comparable with the ambipolar diffusion length. The cases of layers of extrinsic and intrinsic types of conductivity with a linear coordinate dependence of band-gap are analyzed in detail. The layers are assumed to be subjected to illumination by highly absorbed light from the wide-gap surface. It is shown that, due to the presence in the photovoltage of both the field and Dember components, sign inversion points may occur on the spectral dependence of the photovoltaic effect. The possibilities of practical use of the specific features of the photovoltaic effect in thin variable-gap layers on the basis of CdHgTe solid solution are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.