Thermochemical conversion processes of combustion and gasification are operated at comparably high temperatures to achieve a significant conversion of the organic components. Biomasses are providing a low CO2 footprint and in contrast to coals they are also known for their challenging ash systems depending on the particular type of biomass and its place of origin. The components of alkali and alkali earth metals (K, Ca, Mg), phosphorus (P), and halides (Cl) are frequently contained to a large extent in biomass ashes, while some of those are causing the formation of different kinds of deposits – ranging from fouling over sintering up to slagging depending on temperature and related formation of liquid slag. The presence of sintering reactions will usually lead to practical problems in the plants, e.g., reduced heat transfer, enhanced corrosion, and higher demands of cleaning. In other processes, for example in internal circulating (INCI) gasifiers, the sintering between particles is desired for the formation of a recirculation zone providing longer particle residence times and higher conversion rates of the feedstocks. Thus, the sintering behavior has to be investigated prior to their practical application in high-temperature conversion processes due to the significant impact of particle sticking/agglomeration on the entire process. In the present study, different agricultural biomasses, inter alia corn straw and rice husks, are examined in detail. Their ashes are investigated by means of X-ray fluorescence (XRF), X-ray diffraction (XRD), and ash fusion tests (AFT). Ash pellets are treated at different temperatures and cold compression strength tests are performed on those samples to identify the presence of sintering reactions. The temperature-treated ash samples are analyzed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). All experimental results are supported by thermochemical modelling using the FactSage™ software package. Based on the obtained results, the sintering behavior of the ashes and the underlying chemical reactions are determined and cross-compared for all investigated feedstocks. The applicability of the studied biomasses for various types of high-temperature conversion processes is evaluated. For these kinds of applications, potential process-limiting effects caused by sintering are estimated and if necessary suitable temperature ranges and process conditions will be derived.