A multilayer structure based on low-temperature LT-GaAs with crystallographic orientation (111) A is proposed for the fabrication of terahertz (THz) photoconductive antennas. The structures contain active layers of undoped LT-GaAs and high-temperature GaAs:Si layers doped with Si acceptors. At an optical pump power of 19 mW and a bias voltage of 30 V, a photoconductive antenna on an optimized {LT-GaAs / GaAs: Si} (111) A structure emitted THz pulses with an average power of 2.3 μW at a pulse repetition rate of 80 MHz, the conversion efficiency was 1.2 ∙ 10-4. It is shown that the dependence of the integrated power of THz antenna pulses based on {LT-GaAs / GaAs: Si} (111) A structures on the applied voltage is superlinear, and on the optical pump power it has the form of a saturation curve. The possibility of practical application of the obtained antennas for the tasks of terahertz spectroscopy of biological solutions is shown.