The heat produced from the electrochemical reaction in a fuel cell is worth studying, the heat recycled make the fuel cell more efficiency, especially in a high-temperature proton exchange membrane fuel cell (HTPEMFC). In low temperature PEMFC system, the heat is removed by cooling system avoid the membrane degradation exceed 100 degrees C. But in HTPEMFC system, the membrane can afford higher temperature (T-g 420 degrees C), means the cooling system could be removing and through changing the inside flow field to uniform the unit cell temperature in stack. In this study, a 50-100 W HTPEMFC stack is demonstrated and a micro sensor was integrated with the HTPEMFC stack for in situ measurements during the experiments. The results show that when the stack is operated at low and high current loads, the heat generation from the fuel cell causes noticeable changes in the cell temperature, especially in the middle of the stack. In the middle cell of the stack, the temperature exceeds the operating temperature (160 degrees C) by 10-30 degrees C when the current increases. Moreover, changing the flow field to counter-flow or co-flow with U- or Z-type flow fields causes changes to the thermal balance in the stack. The performance, however, remains almost the same for each type of flow field when there is no water affecting the HTPEMFC, even though the change in thermal balance in the stack still occurs. The results of the micro sensor in situ monitoring for each type of flow field displayed higher temperatures on the middle cells. If the waste heat is appropriately used, the high-temperature fuel cell will then be more efficient than the low-temperature fuel cell. The results also show that, in the HTPEMFC stack, the heat generated from the fuel cell can be reused in other ways. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.