Abstract: The CIGS/CdS p-n junction thin films were fabricated and deposited at room temperature with rate of deposition 5, and 6 nm sec–1, on ITO glass substrates with 1mm thickness by thermal evaporation technique at high vacuum pressure 2×10–5 mbar, with area of 1 cm2 and Aluminum electrode as back contact. The thickness of absorber layer (CIGS) was 1 μm while the thickness of the window layer CdS film was 300 nm. The X-ray Diffraction results have shown that all thin films were polycrystalline with orientation of 112 and 211 for CIGS thin films and 111 for CdS films. The direct energy gaps for CIGS and CdS thin films were 1.85 and 2.4 eV, respectively. Atomic Force Microscopy measurement proves that both films CIGS and CdS films have nanostructures. The carrier concentration, Hall mobility and the conductivity of CIGS and CdS thin films were calculated by hall effect measurement showing that p = 3.56×1010 cm–3 and n = 1.76×1014 cm–3, respectively. The J-V characteristics for CIGS/CdS solar cells were measured when illuminated with 1000 W m–2, the efficiency were calculated before and after annealing with temperature 100 200 and 300°C for one hour in vacuum oven. The results indicate that the efficiency decreases with increasing annealing temperature of CIGS\CdS solar cell.