The authors describe some preliminary experimental results of quantum-effect modulation-doped field-effect transistors (MODFETs) with a variety of nanometer gate geometries. The gate geometries were such that various quantum wells and barriers were formed in the channel of the MODFETs through the field effect imposed by the novel gate structures, and the transport of the electrons was affected by resonant tunneling. The devices were fabricated using a combination of molecular beam epitaxy and electron beam lithography. Electrical measurements of the devices at 4.2 K showed resonant tunneling effects and, in particular, showed that resonant tunneling is more pronounced for a system of quantum wells confined in three dimensions than in two. For these quantum effects to be appreciable at practical temperatures, about 77 K, the feature size of the gate geometries should be smaller than 50 nm.>