Electric field effects on the electronic characteristics of semiconductor heterostructures used in recent field effect transistors (FETs) and in a finite superlattice are numerically simulated. This field is due to a voltage bias applied on a Schottky contact. These heterostructures have two-dimensional quantum wells and layers which can be stressed due to different lattice parameters of the materiais involved. Through a numerical self-consistent procedure, many physical quantities are studied, such as the eigen-states and the electronic densities at the sub-bands. The changes in such quantities are associated to the capacitance and to the intrinsic transconductance, as a function of the gate voltage. The results are compared to experimental data. This procedure allows the comprehension of the quantum, phenomena involved and the prediction of device characteristics, without the need to fabricate and test it.