A GaAsn+iδp+in+bulk barrier transistor with an ultra-thinp+Al0.2Ga0.8As base was fabricated by molecular beam epitaxy. It is found that the barrier height can be modified by the ΔEcfor the conduction band barrier and by the ΔEvfor the valence band barrier, in addition to the planar doped bulk barrier. Both the base-emitter bias voltage and the incident light intensity can modulate the collector current.