The effect of emitter grading on the injection barrier of Al0.3Ga0.7As/GaAs heterojunction bipolar transistor grown by metalorganic chemical vapor deposition was studied. The barrier height for electrons injected from the emitter was determined from the temperature dependence of collector current. It has been directly confirmed that the barriers for graded heterojunction and GaAs homojunction are comparable. However, the grading enhanced the recombination at the emitter‐base depletion region, which suggests that the hole confinement was reduced.