The electrical properties of a (100) InP surface were studied based on the fabrication process of a buried heterostructure (BH) laser diode (LD). The current–voltage (I–V) and capacitance–voltage (C–V) characteristics were measured for Schottky barriers on the surface at each step of the process—reactive ion etching (RIE) with a mixture of methane (CH4) or ethane (C2H6) and hydrogen (H2), oxygen plasma treatment, chemical etching, and annealing—under conditions which produce almost the same surface as that immediately before the BH regrowth. From the characteristics, it was found that CH4/H2 and C2H6/H2 RIEs caused the appearance of almost the same damage layers as a result of phosphorus desorption and hydrogen passivation in the near-surface region. Furthermore, it was found that only annealing can remove the hydrogen passivation. These results suggest that to obtain a high-quality regrowth interface it is essential to chemically etch the damage layers resulting from phosphorus desorption prior to BH regrowth in the fabrication process of BH-LDs. © 1997 American Vacuum Society.