Growth temperature (TG) dependence of the acceptor concentrations (NA) in Al0.1Ga0.9Sb grown by liquid phase epitaxy in a very wide growth temperature range (250-500 °C) was investigated. It was found that NA varies with TG down to 350 °C as NA ∝exp(Ea/kBT G) with Ea=0.47 eV and that below 350 °C NA fluctuates depending highly on growth conditions. Acceptors in Al 0.1Ga0.9Sb grown above 350 °C were concluded to be intrinsic. These observations were successfully made using the improved extremely low-temperature growth process. The evaluation technique of measuring the impurity concentration in a thin epitaxial layer on the conductive GaSb substrate by C-V characteristics of metal-insulator-semiconductor structures was employed.