The effect of orientation on self‐aligned source/drain planar GaAs Schottky barrier field‐effect transistors (FET’s) has been investigated. The dependence of the threshold voltage of FET’s on gate length was measured for FET’s oriented in two perpendicular [110] directions. Both stress‐enhanced lateral spread of implanted ions and lateral diffusion at the gate material/GaAs interface are proposed as possible mechanism to account for the orientation effect. The experiments indicate that the preferred direction for the self‐aligned FET fabrication on a (100) substrate is [011¯].