This paper investigates the start-up or warm-up process of a high-temperature proton exchange membrane fuel cell (HT-PEMFC) from room temperature to a desired temperature of similar to 180 degrees C. The heating strategy considered in this study involves an initial heating of the HT-PEMFC by a process referred to as inlet gas heating to a temperature above 100 degrees C. After the fuel cell reaches above 100 degrees C, a voltage is applied, where electrochemical reaction heating is expected to contribute to the heating process. Thus, a numerical transient non-isothermal three-dimensional model is derived to mimic the start-up process. Operational parameters such as anode inlet temperature, cathode inlet temperature, applied voltage and voltage application temperature are varied and their effects on the maximum temperature in the membrane electrode assembly (MEA) and temperature difference in the MEA are studied. Firstly, the distribution of temperature along the channel length indicates an increase of temperature during gas heating and as the voltage is applied at the voltage application temperature, the temperature increases at the centre of the MEA due to exothermic reactions. The two-dimensional temperature distribution indicates a temperature difference between the centre of the MEA and the regions below the bipolar plate where the temperature is relatively lower. Considering the whole start-up process with respect to time, the temperature difference exists throughout the process. This will be the key focus in the parametric study. The parametric study indicates that the inlet gas temperatures, applied voltage and the voltage application temperature affect the maximum temperature in the MEA and most importantly, the temperature difference in the MEA. This can cause thermal stresses to build-up if the increase rate of temperature difference is excessive. Setting the applied voltage high (thus, lower current density) is necessary to reduce the increase rate of temperature difference. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.