The Monte Carlo particle model of GaAs Schottky-barrier field-effect transistors developed at Reading has been applied to describe a new f.e.t. geometry in order to establish the noise performance. The effect of introducing ap-type layer between the epilayer and the substrate is examined and the d.c. characteristics obtained are presented. By varying the thicknesses of both the epilayer and the buffer layer, as well as the doping of the latter, an optimal design has been arrived at. However, the transconductance of this optimal design is very sensitive to the thickness of the epilayer.