We have developed a new system for reflection high-energy electron diffraction (RHEED) with two pairs of magnetic coils to measure rocking curves in a short time. Since the measurement time of the system is short and the intensity measurement is very accurate compared with mechanical angle adjustment systems currently in use, this system is the most suitable tool to determine structural phase transitions at high temperatures. For the Si(1 1 1)surface, we have discovered an additional phase just below the melting temperature, in which the thermal vibration of surface atoms is strongly enhanced. For the Si(0 0 1) surface, the asymmetric dimer structure, which is believed to be the most stable at low temperature, transforms into the symmetric dimer structure, as confirmed by comparison with a rocking curve from a hydrogen-terminated Si(0 0 1) 2 x 1 surface. (C) 2004 Elsevier B.V. All rights reserved.