Abstract
A new type in‐plane gated field effect transistor where the semi‐insulating substrate itself is used as a gate insulator region is proposed. n‐ and p‐type in‐plane gated field effect transistors are fabricated on a semi‐insulating GaAs substrate by focused ion beam scanning of Si++ and Be++, respectively. These in‐plane gated field effect transistors are found to operate well at room temperature.