In this paper, the temperature coefficient of 4H-SiC NPN BJT current gain is studied by way of numerical simulations. In general, 4H-SiC NPN BJT would have a positive temperature coefficient (PTC) for the common emitter current gain if the acceptor ionization energy is smaller than 170 meV. Both PTC and negative temperature coefficient (NTC) can occur in 4H-SiC NPN BJT with an aluminum-doped base. High base doping concentration is required to obtain a wide range of current density with a NTC for current gain, especially when the electron lifetime in base is low. For a base doping concentration of 2.5 x 10(17) cm(-3), the NTC for current gain is obtained for current density up to 300 A/cm(2), even when the electron lifetime is as low as 48 ns. The experimental results are also reported. (C) 2002 Elsevier Science Ltd. All rights reserved.