The response of a 300-µm-thick silicon detector to an incident polyenergetic neutron beam has been evaluated by the use of analytical techniques. The analysis indicates that for neutrons <6 MeV the response of a 300-µm silicon detector to neutrons emanating from a plutonium dioxide (RTG) heat source is basically due to elastic scattering reactions and the contribution from other reactions, i.e., (n,p) and (n,α), is <2%. The contribution from radiative reactions, i.e., (n,γ) and (n,n′γ), is even smaller and therefore is ignored. For neutron energies up to 6 MeV, the maximum response for a 300-µm silicon detector is <4 × 10−3 counts/n within the range of bias energies 25 to 250 keV. If the effects of pulse height defect and the true angular distribution of scattered neutrons are included, the response will be reduced to 1.3 × 10−3 counts/n.