Grain‐boundary capacitance versus voltage, current versus voltage, and capacitance transient measurements are reported on lightly dopedn‐type GaAs bicrystals. The measurements are analyzed in terms of the abrupt depletion edge model in which the dominant current mechanism across the potential barrier formed by trapped charge at the interface is thermionic emission. The steady‐state measurements are completely consistent with this model and provide grain‐boundary parameters (barrier height, net carrier concentration in adjacent grains, and interface charge) necessary for interpreting capacitance transient measurements. The latter, made on a bicrystal specially selected for uniformity of the grain‐boundary barrier, reveal the presence of two closely spaced levels at 0.62 and 0.74 eV below the conduction band edge. The capture cross section associated with the dominant lower level is measured directly by two methods and falls in the range 10−14–10−13cm2.