Multi-junction solar cells, particularly those utilizing III–V semiconductor materials, offer high conversion efficiency by employing multiple P-N junctions with different band gap energies to capture specific wavelengths of sunlight. Among these, the triple-junction photovoltaic cell, comprising Indium Gallium Phosphide (InGaP), Indium Gallium Arsenide (InGaAs), and Germanium (Ge) subcells, stands out for its efficiency. However, temperature variations significantly impact the performance of these subcells, necessitating a comprehensive understanding of their thermal behavior. In this study, we employ PyAMS (Python for Analog and Mixed Signals) software to model and simulate the behavior of InGaP/InGaAs/Ge sub cells under varying temperature conditions. Through comparison with experimental data, we validate our model and analyze key performance parameters, including short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), and overall efficiency (η). Our findings reveal minimal changes in short circuit current density with temperature, while the open circuit voltage exhibits a substantial decrease beyond 60°C when exposed to concentrated illumination of 10 Suns, significantly impacting fill factor and efficiency. By elucidating the thermal behavior of three-junction solar cells, our study contributes valuable insights for designing and implementing cooling systems, thereby enhancing the performance and reliability of photovoltaic systems in practical applications.