Static microindentation as well as dynamic displacement-sensitive indentation (DSI) tests have been performed between RT and 450°C on the (001) surface of undoped GaAs. In the static tests, the 4-fold symmetry reduces to 2-fold symmetry in some studied range of temperatures. The temperature dependence of the indentation diagonal and the crack length has been measured and, from disappearance of indentation cracks, the indentation brittle-to-ductile transition (IBDT) temperature T IBDT has been estimated. It is found that the temperature at which a transition in the energy density in DSI tests occurs nearly coincides with T IBDT as measured by static indentation tests; for undoped GaAs, both these temperatures are in the range of 200-225°C. This is about 100°C lower than the true brittle-to-ductile temperature T BDT, as measured by 4-point bending tests. The difference between T IBDT and T BDT is explained in terms of the superimposed hydrostatic stress component in the indentation experiments, and the crack asymmetry around the indentations is interpreted in terms of the different mobilities of α and β dislocations in GaAs.