High Electron Mobility Transistor (HEMT) LSI technology based on selectively doped GaAs/AlGaAs heterojunction structure for high speed computer application is described. Diagnostic patterns including HEMT test device groups are fabricated to encompass a number of interrelated material and device processing parameters. By evaluating the gate length dependence of threshold voltage and K-factor of short channel HEMTs and their uniformity over the wafer, HEMT is confirmed to be suitable for high performance LSI devices. Master-slave flip-flop divide-by-two circuits are implemented, operating at clock frequencies as high as 8.9 GHz with power dissipation of 2.8 mW/gate at 77K. This corresponds to a logic delay of 22 ps/gate, roughly three times faster than that of GaAs MESFET technology. The top down design of the HEMT based computer is performed. System performance is projected to a system clock cycle time of 2 ns to achieve computer performance of over 120 MIPS.