Summary: Heat transfer between surfaces at close vicinity has important applications in nanoscale energy conversion devices and near-field scanning thermal microscopy. The present paper describes a comprehensive investigation of the radiation energy transfer between two semi-infinite parallel plates at different temperatures, involving silicon with varying dopant concentrations, when the distance of separation is from \(10 \mu \)m down to 1 nm. The net radiation heat flux is calculated by means of the fluctuational electrodynamics. The dielectric function of silicon is modeled using a Drude model, considering the effects of temperature and doping level on the carrier concentrations and scattering times. The calculated results show that the dopant concentration strongly affects the radiation heat flux when the two media are separated at nanometer distances. For heavily doped silicon plates separated at a distance of 1 nm, the present study predicts a radiation energy flux of over five orders of magnitude greater than that between two blackbodies placed far apart. Furthermore, the radiation energy flux can be more than ten times larger than the conduction heat flux of air at the atmospheric pressure, and the radiation heat transfer coefficient may exceed 1 MW m\(^{-2}\) K\(^{-1}\). The theoretical understanding gained from the present research will facilitate the design of experiments that utilize near-field radiation to enhance heating or cooling at the nanoscale for applications such as thermal control in nanoelectronics, energy conversion, and nanothermal probing and manufacturing.