Photomodulation spectroscopy studies of the transitions at the Γ point of the Brillouin zone of thin films of BxGa1-xAs alloys grown by metal-organic chemical-vapor deposition are presented. A very small increase of the fundamental band gap is found in samples with B content up to 3%. Under hydrostatic pressure, the band gap increases at a rate almost identical to the pressure dependence of the GaAs band gap. In contrast to the case of N incorporation at similar concentrations into GaAs, the experimental results show that B incorporation does not cause large modifications of the conduction-band structure in BxGa1-xAs alloys. © 2003 American Institute of Physics.