Cyclotron resonance and photoluminescence measurements were carried out on two types of modulation-doped field-effect transistor heterostructures whose channels were made of an InAs–GaAs short-period superlattice and of anInxGa1−xAsquantum well, respectively. From cyclotron resonance data a linear dependence of the channel electron effective mass on indium content was obtained for both series of samples. For a given mean value of the indium content in the channel, the effective mass is found to be systematically higher in samples where the channel is based on a short-period superlattice rather than on an alloy-based channel. This can be attributed to larger nonparabolic effects in the former. Calculations of nonparabolicity corrections are in agreement with these results. In our theoretical model, the energy of the electron and heavy hole levels were determined self-consistently.