Neutron radiation detector for nuclear reactor applications plays an important role in getting information about the actual neutron flux. Such a detector must be able to operate at high neutron flux levels (>10 9 cm −2 s −1 ) and discriminate the neutron and gamma responses in the nuclear reactor's mixed neutron-gamma environment. Silicon carbide and diamond are the most attractive semiconductor materials for neutron detection, thanks to their outstanding properties, such as high displacement threshold energy and wide bandgap energy, which allow them to operate in high radiation levels and high temperature. The aim of this article is to compare the ability to detect thermal neutrons of these two semiconductors at the same irradiation conditions. For this purpose, the neutron irradiation tests of detectors were implemented at MINERVE research reactor at CEA Cadarache. The 4H-silicon carbide (SiC) p + n diode has demonstrated better neutron-gamma discrimination at 0-V bias voltage than at −200 V which is explained by its increased sensitivity to gamma photons at −200 V caused by a wider charge collection region than at 0 V. Therefore, it is preferable to use the 4H-SiC p + n diode without an external electric field for applications in the mixed neutron-gamma environment such as nuclear reactor environment. The results show that the single-crystal chemical vapor-deposited (sCVD) diamond-based detector has better neutron to gamma discrimination, thanks to the use of 6 Li as a neutron converter instead of 10 B. However, the study of the radiation stability of detectors showed that the sCVD diamond-based detector suffers from the "polarization effect" when it operates at a high neutron flux (~10 9 cm<inline-formula> <tex-math notation="LaTeX">^{-2}\,\,\cdot \,\,\text{s}^{-1} </tex-math></inline-formula>).