Room‐temperature Hall mobility as a function of pressure (0–8 kbar) has been measured for high‐purity liquid‐phase‐epitaxy‐grown Ga1−xAlxAs layers. GaAs‐like band structure of low‐composition alloys has also been converted to Si‐like band structure at high pressures and the Hall mobility measured as a function of temperature (77≲T≲300 °K) with crystals locked under constant pressures. The data have been analyzed to identify and distinguish the presence of space charge and alloy scatterings both characterized by mobilities limited byT−1/2. The space charge scattering has been found to be absent in all the crystals studied exceptx=0.047. The alloy scattering potential for electrons in the &Ggr; minimum has been shown to depend on the alloy composition with a maximum value of 1.56 eV atx=0.19. For electrons in theXminima, this potential has been found to be independent of composition with a value of only 0.4 eV.