Monte Carlo simulation is carried out to investigate the high-field transport properties of the two-dimensional electron gas in strained Si/SiGe heterostructures. In the simulation we take into account the intervalley scattering between twofold and fourfold valleys of an Si well layer split by the tensile strain. Intervalley scatterings within the twofold or fourfold valleys are also incorporated in the simulation as well as the acoustic phonon scattering. We obtained an electron drift velocity at room temperature as high as 1*107 cm s-1 at 10 kV cm-1. Calculated results of 4.2 and 77 K show negative differential mobility beyond 10 kV cm-1. At 77 K the transient response of the drift velocity shows a remarkable overshoot, reaching about 3*107 cms-1 at 0.2 ps at 10 kV cm -1.