High–temperature proton exchange membrane fuel cells (HT–PEMFCs) are widely recognized as a feasible sustainable energy technology for usage in automotive and stationary applications. It has high CO tolerance, fast reaction kinetics, a high amount of reusable heat energy, and no humidification requirement due to the operating temperature higher than 100˚C, thus the water at the inlet and the chemical reaction’s products become the vapor phase, leading to simple water and thermal management. However, various factors influence the performance of high–temperature membrane electrode assemblies (MEAs) with phosphoric acid–doped PBI membrane, therefore determining the optimal operating parameters is one of the challenges for an HT–PEMFC. This study investigated the performance of HT–PEMFCs at various temperatures (140, 160, and 180˚C), air cathode stoichiometric ratio (2, 2.5, and 3), acid doping levels (360 and 460%), and gas diffusion layers (GDL340, GDS with 5 and 20% PTFE). The catalyst layer was composed of Pt/C (46.6 wt. %), PVDF binder, and DMAc as a solvent. The Pt loading on the electrode was approximately set as 0.5 and 1 mg Pt·cm–2 for the anode and the cathode, respectively. The commercial PBI membrane was utilized in this study. The results indicated that increasing the operating temperature can enhance the performance of an HT–PEMFC. However, the cell performance also increased with increasing the air stoichiometric ratio at the cathode side and the acid doping level. Moreover, the MEA with GDS310 reached the maximum power density up to 0.410 and 0.396 W·cm–2, which can be enhanced by approximately 31% and 27% under 5 and 20% PTFE, respectively.