Abstract: Electron transport properties in GaSb and GaAs are calculated for different temperature, doping dependencies at high electric field applications. The calculations are performed using a three valleys ensemble Monte Carlo model that includes numerical formulations of the phonon scattering rates and ionized impurity scattering rates. For two materials, it is found that electron velocity overshoot only occurs when the electric field in increased to a value above a certain critical field. This critical field is strongly dependent on the material parameters. Results from the two materials are finally compared. The agreement with the available experimental data is found to be satisfactory.