In this study, a concentrated solar thermal power plant (CSP) with parabolic trough collectors integrated into a reference triple-pressure NGCC power plant as an Integrated Solar Combined Cycle (ISCC). The aim is to study and assessment the overall performance of different hybrid schemes of ISCC plants. Thus, A detailed thermodynamic model of the proposed ISCC plants has been developed to investigate the thermodynamic impact of solar heat rate injected in the high and intermediate pressure sections (HP, IP) of the NGCC plant at different seasons of the year. The cycles have been characterized and simulated under southern Egypt climate. An increase in the NGCC output power of 52.315 MWe with peak net thermal efficiency of 64.86% and solar to electric conservation efficiency of 46.95% are obtained from the integration process in the HP section. The increase in power output reaches a limit of 43.38 MWe with a net efficiency of 63.82% and solar to electric efficiency of 38.85% for integration in the IP section. The results of the analysis have been indicated that the higher the solar energy injected the higher is the solar electricity production and the higher is the overall thermal efficiency.