The Pt/GaAs Schottky interfaces with excellent qualities were fabricated by a novel in situ electrochemical etching and plating technology using the electrical and photo pulses. The etched GaAs surface was very smooth, and no oxidized and disordered layer was produced at the interface. This technology also prevents formation of process-induced near-surface defect levels of GaAs. The Pt/GaAs diodes exhibited nearly ideal thermionic emission characteristics with a barrier height larger than 1.0 eV and an ideality factor lower than 1.05. Selective deposition of Schottky barriers to the edge of a two-dimensional electron gas in a GaAs/AlGaAs quantum well structure was truly achieved by this process, which is confirmed by the agreement of the experimental C-V results with theoretical predictions, as well as the results of the electron beam-induced current measurements.