We have performed measurements of carrier concentration and Hall mobility, between 4.2 K and room temperature, in InGaAsP (energy gap of 0.96 eV) epitaxial layers grown on semi‐insulating InP. It is shown that for this kind of material in the range of concentration studied (2.0×1016–1.6×1018cm−3), alloy scattering has to be taken into account as a mechanism limiting the mobility even at low temperatures. Also, in the entire range of temperature and concentration studied, Fermi‐Dirac statistics are better suited than Boltzmann statistics for theoretical calculations of Fermi energy, because even for concentrations as low as 2.0×1016cm−3, the material is degenerated at low temperatures. Following these assumptions, we have calculated the alloy scattering potential as being between 0.52 and 0.62 eV.