The conduction and interface states of laterally wet-oxidized GaAs-AlGaAs-GaAs structures after various oxidation times are investigated. Effective current blocking is achieved after 150 min oxidation and the conduction of current through the oxidized AlGaAs layer is controlled by the Poole-Frenkel mechanism, from which a relative dielectric constant of 7.07 is obtained. At an oxidation time of 15 min, capacitance-voltage spectra exhibit capacitance dispersion over frequency, implying the presence of an interface state. The intensity of the dispersion increases with increasing the oxidation time and admittance spectroscopy reveals a significant interface state at ∼0.28 eV at 45 min. Further increasing the oxidation time to 150 min broadens the interface state to a set of continuous interface states from 0.19-0.31 eV with decreasing densities from 3× 1011 to 0.9× 1011 eV-1 cm-2 and generates fixed charges of about 9.1× 1011 cm-2 in the oxidized layer. By comparison to a similar trap in a relaxed InGaAsGaAs, the interface state is tentatively assigned to the interaction of residual As with dislocations.