Ion‐implanted MOS transistors were fabricated and their electrical characteristics, such as threshold voltage, effective mobility, etc., were measured. In the11B+‐implantedp‐channel case, threshold voltageVTcan be shifted linearly with implant dose. These shifts &Dgr;VTwere entirely determined by the net dose entering silicon. On the other hand, in the11B+‐implantedn‐channel case, threshold voltage shift &Dgr;VTvaried sublinearly with dose and showed strong dose profile dependence. The profiles were varied with changing implantation energies and annealing times. These results can be interpreted in accordance with the rapid decrease of the maximum surface depletion layerXdmaxwith the implant dose increase. Numerical calculations of threshold voltage shifts accounting for nonuniformly implanted profiles were compared with observed results. Good agreement was obtained. Effective mobilities &mgr;effof11B+‐implantedp‐ andn‐channel MOS transistors also showed different dose dependences. In the low‐dose region, effective mobilities of11B+‐implantedp‐channel MOSFET remained almost unchanged, but those of then‐channel case decreased monotonically with dose increase. Qualitative arguments, taking into account surface scattering and impurity scattering effects, and rough calculations are presented.