The electroluminescence signal emitted from operating InP-based heterojunction bipolar transistors (HBT) is analyzed, giving clear evidence of ballistic electron transport through the base. The luminescence signal is studied as a function of base thickness, providing direct access to the ballistic electron mean free path. This continuous wave technique proves to be very efficient to measure ballistic electron scattering rates: 30 fs at 77 K and 19 fs at 300 K for a base Be doped to1019 cm−3.Quasiballistic transport range is found to be comparable to base width accessible by state of the art device technology, demonstrating its importance for ultrafast HBT operation. ©1998 American Institute of Physics.