Reduction of the density of protrusions on a cleaned GaAs surface by arsonic-free high-temperature surface cleaning performed in the preparation chamber of a molecular beam epitaxy system was investigated. The density of protrusions was found to decrease when the temperature ramp-up rate of the substrate was reduced from 10 degreesC/min to 1 degreesC/min. Using a constant ramp-up rate of 1 degreesC/min required approximately 10 h to reach 650 degreesC, Consequently, a new two-step-heating sequence is proposed, in which the ramp-up, rate is changed from 10 degreesC/min to 1 degreesC/min at 575 degreesC and the total ramp-up time is reduced to 3 h. The roughness of the surface cleaned using the two-step-heating sequence was studied by atomic force microscopy and was found to be almost identical to that for the constant ramp-up rate of 1 degreesC/min. X-lay photoelectron spectroscopy revealed that the stoichiometry of the cleaned GaAs surface was maintained and no excessive Ga was present on the surface. Thr electron mobility of two-dimensional electron gas in high-electron-mobility transistor grown on the GaAs substrate cleaned using the two-step-heating method increased at low tel temperatures by 50% beyond that grown on GaAs substrate that was cleaned using a constant ramp-up, rate of 10 degreesC/min.