The sign of the majority photocarriers in semi-insulating iron-doped InP and undoped GaAs containing EL2 centres illuminated at 1.06 μm is unambiguously determined from the direction of beam coupling in a two-wave photorefractive mixing experiment previously applied to ferroelectric crystals. Majority photocarriers in these InP:Fe and GaAs:EL2 crystals are found to be electrons.