A high transconductance of 602 mS/mm has been obtained in 0. 3 micrometer-long gate GaAs MESFETs using a combined sidewall-assisted self-alignment technology and WSi//x gate n** plus selective ion implantation technology. The gate orientation effect for the fabricated FET is enhanced by lateral diffusion of implanted n** plus impurities to the channel region. 25-stage ring oscillators with an E/D DCFL configuration were also fabricated using 0. 7 micrometer-long gate FETs. The minimum propagation delay time of 16 ps/gate was observed.