Lattice-matched N-p + -n In 0 . 4 9 Ga 0 . 5 1 P/GaAs heterojunction bipolar transistors (HBT's) with heavily beryllium doped base and undoped spacers were grown by gas source molecular beam epitaxy (GSMBE). The epitaxial structure consists of, from the bottom to the top, a 5000Å n + -GaAs sub-collector with Si doping level of 3x10 1 8 cm - 3 , a 7000Å n-GaAs collector doped at concentration of 3x10 1 6 cm - 3 , a 60nm p + -GaAs base with Be doping level up to 3x10 1 9 cm - 3 inserted between two undoped GaAs spacers, a 100nm N-In 0 . 4 9 Ga 0 . 5 1 P emitter doped at 3x10 1 7 cm - 3 . The structure was completed with a 150nm n + -GaAs cap layer with Si doping level of 3x10 1 8 cm - 3 . Devices with emitter area of 100x100μm were fabricated on the grown wafer by using selective wet chemical etching technique and photolithographic process. AuGeNi/Au was used for the emitter and collector contacts, and Cr/Au was used for the base contact. The turn-on voltages of p + -GaAs/N-In 0 . 4 9 Ga 0 . 5 1 P heterojunction and p + -GaAs/n-GaAs junction are 1.0 and 0.65V. The reverse breakdown voltages of the B-E and B-C junctions are 10 and 12V. The common-emitter current-voltage characteristics show that the maximum current gain reaches 320 at the collector current of 90mA.