An interesting InGaP/GaAs resonant-tunneling heterojunction bipolar transistor incorporating a superlattice (SL) structure in the emitter has been fabricated and studied. With the n-type doped well, the strongly coupling effect dominating the biased SL behaves like a double barrier operation. On the basis of the transfer matrix method, the transport mechanism of sequential miniband conduction can be developed by the theoretical calculation associated with the RT in the studied SL structure. Experimentally, the double negative differential resistance phenomena are presented both in the two-and three-terminal current-voltage characteristics at 300 K. In addition, excellent transistor behaviors including the high dc current gain as high as 70, low saturation voltage smaller than 1.2 V, low offset voltage of 110 mV and high breakdown voltage larger than 20 V are obtained.