Germanium (Ge) nanoclusters are grown by a molecular-beam epitaxy technique on chemically oxidized Si(100) surface at 700ºC. Evidence for long-term photoinduced changes of surface conductivity in structures with Ge nanoclusters (NCs) grown on silicon oxide is presented. Photoexcitation NCs or Si by quanta with different energy allows observing two non-equilibrium steady-states with excess and shortage of conductivity values as compare to equilibrium one. The persistent photoconductivity (PPC) behaviour was observed after interband excitation of electron-hole pairs in Si(001) substrate. This effect may be attributed to spatial carrier separation of photoexcited electron-hole pairs by macroscopic fields in the depletion layer of near-surface Si. Photoquenching of surface conductivity, driven by optical recharging of Ge NC’s and Si/SiO2 interface states, is observed. Conductivity decay is discussed in the terms of hole`s accumulation by Ge-NC states enhancing the local-potential variations and, therefore, decreasing the surface conductivity of p-Si.