Intrinsic carrier density of 4H-SiC was experimentally derived from 294 to 595 K by analyzing a collector current in an npn-type SiC bipolar junction transistor (BJT). The obtained intrinsic carrier density was in good agreement with the theoretical value calculated taking account of the multiple and non-parabolic SiC bands. The temperature dependence of bandgap was also estimated from the deduced intrinsic carrier density, where the bandgap shrinkage at high temperatures was confirmed.