The high-voltage p+–p0–i–n0–n+ structures based on epitaxial gradual GaAs p0–i–n0 junction grown in hydrogen or argon atmosphere have been studied by capacitance-voltage spectroscopy and deep-level transient spectroscopy, DLTS, before and after neutron irradiation. After neutron irradiation, the broad bands associated with electron emission from the states lying above midgap appear in DLTS spectra of both p0–i–n0 GaAs structures. It is assumed that the carrier emission mechanism in the neutron-irradiated GaAs is the same as that in amorphous materials.