A new approach for hybrid metal-insulator-semiconductor (MIS) Si solar cells is adopted by Institute of Fundamental Problems for High Technology, Ukrainian Academy of Sciences. In order to interpret the effect of illumination and Co-60 gamma-ray radiation dose on the electrical characteristics of solar cells are studied at room temperature. Before the solar cells are subjected to stressed irradiation six different illumination levels of forward and reverse bias I-V measurements are carried out at room temperature. The solar cells are irradiated with Co-60 gamma-ray source irradiation, with a dose rate of 2.12 kGy/h and an over dose range from 0 to 500 kGy. Experimental results shows that both the values of capacitance and conductance increase with increasing illumination levels and give the peaks at high illumination levels. gamma-ray irradiation induces an increase in the barrier heights Phi(b)(C-V) which are obtained from reverse-bias C-V measurements, whereas barrier heights Phi(b)(I-V) which are deducted from forward-bias I-V measurements remain essentially constant. This negligible change of Phi(b)(I-V)) is attributed to the low barrier height (BH) in regions associated with the surface termination of dislocations. Both the I-V and C-V characteristics indicate that the total-dose radiation hardness of the Si solar cells cannot be neglected according to illumination levels. (C) 2007 Elsevier Ltd. All rights reserved.