A semiempirical method allowing description and normalization of the prompt fission neutron spectrum (PFNS) is proposed. The method is based on the assumption that PFNS 235U(nth,f) and 252Cf(SF) have similar shapes. In the case of these two isotopes, the method works with accuracy of 1 to 2% in the energy range of 0.1 to 10 MeV.