Abstract: A high-barrier gate field-effect transistor with an n+-GaAs/p+-GaInP/n-GaAs heterojunctions has been fabricated. The channel contains tri-step doped GaAs layers with a different doping level and thickness in each layer. Due to the significant conduction band discontinuity &Dgr;EC between GaInP/GaAs heterointerface in the gate region, the gate barrier is increased and electrons are effectively confined in the channel. Furthermore, the existence of a valance band discontinuity &Dgr;Ev at the GaInP/GaAs heterointerface may prevent holes generated by impact ionization from reaching the gate region. The tri-step doped channel is adopted to increase the output current and linear transconductance. Therefore the device of this invention provides a high gate-drain breakdown voltage, a low leakage current and a high transconductance. Based on these advantages, the proposed device shows the promise for high-power, large signal analog, and digital switching circuit applications.