Uniaxially stressed Si is used in current leading edge logic technologies, because it can increase the mobility and current drive of both n-channel and p-channel MOSFETs. While biaxially strained inversion layers have often been subject to theoretical investigations, the technologically more interesting application, with process-induced uniaxial stress along the channel direction, has surprisingly been neglected. In my present work the origin of the electron inversion layer mobility enhancement on (001) and (110) wafers with uniaxial stress was investigated. It was shown experimentally that uniaxial stress leads to a pronounced in-plane mobility anisotropy for both substrate orientations. While on (110) substrates this effect stems from the ellipsoidal shape of the lowest subband ladder, an effective mass change induced by [110] stress has to be taken into account to explain the anisotropic mobility of [110] uniaxially stressed (001) wafers. This effective mass change was successfully reproduced by band structure calculations of Si with arbitrary stress/strain conditions using the empirical non-local pseudopotential method. When uniaxial stress is applied along the [110] axis, one can apply symmetry considerations to determine the irreducible volume (see the figure) of the Brillouin zone, which is six times larger than the irreducible wedge of unstrained Si. Based on these findings the Monte Carlo simulation tool VMC was extended to allow for the simulation of uniaxially stressed Si/Ge, and good agreement between simulation results and experimental data was obtained.