We propose an improved In0.5Ga0.5P/GaAs heterostructure-emitter bipolar transistor (HEBT) grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The recombination at p-n interface can be significantly reduced at low collector current using 100 Angstrom undoped GaAs spacers. Meanwhile, the emitter edge thinning technique is used to reduce the surface recombination current. The passivated device reveals a current gain as high as 360, along with an offset voltage as low as 80 mV. Moreover, the measured results indicate that the current gains vary slowly with temperature. In order to demonstrate that the emitter edge-thinning technique can effectively reduce the surface recombination current, the emitter size effect on current gain is also investigated.