The first trial of in-situ reflection high-energy electron diffraction (RHEED) monitoring of cleaning processes on semiconductor surfaces with hydrogen (H) plasma was performed. The cleaning time on (100) GaAs surfaces decreased for the higher temperature, while that on (100) Si surfaces increased for the higher temperature. This opposite tendency in the temperature dependence was studied with the measured temperature dependence of the etch rate and the in-situ quadrupole mass spectroscopy. The dependence of the Si surface reconstruction on the angle of incidence of the H-plasma beam is also reported for the first time. © 1990 IOP Publishing Ltd.