Using an ensemble Monte Carlo simulation, we study the electron transport properties in tensile strained Si grown on aSi1−xGexsubstrate and in ann-channelSi/Si1−xGexmodulation-doped field-effect transistor (MODFET). Owing to the strain-induced modification of the conduction-band structure, the in-plane drift mobility in undoped material reaches3250 cm2/V sat 300 K (forx⩾0.2) and 31000cm2/V sat 77 K (forx⩾0.05). The two-dimensional Monte Carlo modeling of 0.18 &mgr;m gate Si/SiGe MODFETs reveals a high velocity overshoot of2.5×107 cm/srelated to a significant ballistic transport through the gated part of the strained Si channel. For a 0.18 &mgr;m gate and a Ge mole fractionx=0.3,intrinsic transconductance and transition frequency as high as 460 mS/mm and 85 GHz are obtained. ©1997 American Institute of Physics.