Thermoascus is a genus of soil fungi in the family Trichocomaceae. Species in the genus are characterized by the production of heat-resistant ascospores. Thermoascus was circumscribed by German botanist Hugo Miehe in 1907. The type species, Thermoascus aurantiacus, is of research interest because it secretes heat-resistant hydrolase enzymes that could possibly be used in biotechnological applications, such as the conversion of biomass to biofuels.