The mobility behavior of boron delta (δ)‐doped Si, Si1−xGex(0≤x≤1) is investigated, which includes the first mobility measurements reported for B δ‐doped Si1−xGexand Ge. The expected mobility enhancement from δ doping is not realized in Si:B due to the heavy effective mass of holes. However, some enhancement may be possible at lower doping levels for narrower wells. Indications of mobility enhancement have been realized for δ‐doped Ge:B because of the relatively light effective mass. We also present the implementation of boron δ‐doped layers in the fabrication of (i) the first SiGe:B δ‐FET and (ii) the first coupled δ‐layer Si:B δ‐FET.