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 (H-2), 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/H-2 and C2H6/H-2 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.