The temperature coefficient of 4H-SiC NPN BJT current gain is investigated by way of two-dimensional numerical simulations in this paper. Both positive and negative temperature coefficients in current gain can occur in 4H-SiC NPN BIT with Aluminum-doped base. 4H-SiC NPN BJTs would generally have a positive temperature coefficient if an acceptor with ionization energy level (EA) smaller than 170meV were used. High base doping concentration is required to obtain negative temperature coefficient when carrier lifetime is low.