We studied the electrical properties, the Hall mobility and the free carrier concentration of modulation-doped field-effect transitor heterostructures using M(InAs)mN(GaAs)m short-period superlattice (SPS) channels. We changed the number of monolayers m for InAs, n for GaAs and the numbers M and N of interfaces InAsmGaAsn in the channel. In the SPS, the thickness of the InAs layer was varied from 0.5 ± 0.1 to 1.6 ± 0.1 monolayers (ML) and that of GaAs from 5 to 15 ML. The number M of interfaces varied from 3 to 7 while the number N varied from 2 to 6. The total SPS channel thickness was varied, but always kept below the critical layer thickness calculated from the double kink model derived by Matthews and Blakeslee. The persistent photoconductivity effect, at 77 K, was employed to study the variation of the Hall mobility and free carrier density in the SPS channels. A red light-emitting diode was used as the illumination source. Our results indicate that the Hall mobility increases for (a) a decreasing number of InAsGaAs and GaAsInAs interfaces, (b) on employing an integral number of InAs monolayers, and (c) on employing an increasing number of GaAs monolayers. We believe that they are effective in producing surface smoothing.