The electron velocity in high‐purity germanium at 20 mK has been measured as a function of the electric field in the <100> orientation. A new simulation code, taking into account the key phenomena of ionized impurity and inelastic phonon scattering, has been developed for Monte Carlo modeling of electronic transport in Ge at cryogenic temperatures. The code accounts for the essential features of electron transport, including the hitherto unexplained effect of a negative differential mobility along the <111> field orientation. Experimental data for the electron velocities at 20 mK are reproduced with a satisfactory accuracy.