Currently, researchers are focusing their attention on lowering the cost of electrical energy produced by PV modules. In this regard, solar cells (SC) on the base of semiconductor-insulatorsemiconductor (SIS) structures are very promising as low cost photovoltaic solar energy converters. For their fabrication, it is not necessary to obtain a p-n junction because the separation of the charge carriers generated by solar radiation is realized by an electric field at the insulator semiconductor interface. Such SIS structures are obtained by the deposition of thin films of transparent conductor oxides (TCO) on the oxidized silicon surface. The present communication traces briefly the history of these PV devices, shows the main contemporary results of their investigations and tries to look at possible futures achievements and applications in the area. Initial investigations of ITO/Si SIS structures were carried out in the USA and published in 1976. Basic investigations of ITO/Si SIS structures have been also carried out in the USA (see the works by DuBow et al., 1976; Mizrah et al., 1976; Shewchun et al., 1978- 1979). Theoretical and experimental aspects of the processes that take place in these structures are examined in those papers. Later on the investigations of SC based on SIS structures using Si, InP, CdTe and other semiconductor materials as an absorber component have been globally continued in Japan (Nagatomo et al., 1982; Kobayashi, et al., 1991), India (Vasu & Subrahmanyam, 1992; Vasu et al., 1993), France (Manifacier & Szepessy, 1977; Caldererer et al., 1979), Ukraine (Malik et al., 19791980), Russia (Untila et al., 1998), the USA, Brasil (Marques & Chambouleyron, 1986) and the Republic of Moldova (Botnariuc et al., 1990; Gagara et al., 1996; Simashkevich et al., 1999). Different techniques of TCO layers deposition (R.F. sputtering, spray pyrolysis, electron beam deposition) have been used in the above mentioned works. The major absorbing semiconductor material used was silicon. The analysis of the works referred to shows that the conversion efficiency of ITO/nSi solar cells obtained by various methods on smooth, non-textured Si crystal surfaces, is about 10% and in some cases reaches 12%. Besides silicon, InP (Gessert et al., 1990- 1991), CdTe (Adeeb et al., 1987) and other semiconductor materials have been also used in SIS structures as an absorber component, The optical losses of ITO/nSi solar cells depend on the surface state of wafers surface and can be minimized by creating a textured surface of the light absorbing semiconductor material by means of selective chemical etching; in this case efficiencies up to 12% have been obtained. ITO/nSi and ITO/InP SC have been also fabricated and investigated at the Institute of Applied Physics of the Academy of Sciences of Moldoav. Current-voltage characteristics were studied, mechanisms of the current flow were determined and respective band diagrams were proposed. The optimization of photoelectric parameters was realized. ITO/nSi SC with an enlarged area of up to 48 cm2 have been fabricated, for cells with the area of 8.1cm2 the efficiency was 10.58%.The maximum efficiency of ITO/nSi SC is 12%, but in the case of a textured surface of Si crystals the efficiency is over 15%. InP based SIS structures fabricated by deposition of ITO layers onto pInP crystal surfaces have high efficiencies; in addition, they are easier fabricated in comparison with diffusion junction cells. The maximum efficiency of 11.6% was obtained in the case of fabrication of ITO/pInP/p+InP structures They demonstrate a high radiation stability, that is less than in Si and GaAs based solar cells. A new type of bifacial solar cells n+Si/nSi/SiO2/n+ITO based only on isotype junctions was elaborated and fabricated. It was demonstrated that the simultaneous illumination of both frontal and rear surfaces of the structures allow to obtain an overall current. The technological process of manufacturing such solar cells does not require sophisticated equipment. Bifacial solar cells with the overall efficiency of 21% and bifaciality coefficient of 0.65 have been obtained using a single crystalline silicon with a textured surface as an absorbent material.