We present threshold voltage data for Al0.48In0.52As/Ga0.47In0.53As/InP heterostructure insulated gate FETs (HIGFETs) with gate lengths from 1.2μm to 0.4μm. The refractory-gate, self-aligned fabrication process was applied to MBE-grown structures with 300Å Ga0.47In0.53As channels and semi-insulating superlattice buffers, to achieve sharp pinchoff with excellent threshold uniformity. HIGFETs with L = l.2μm showed a threshold voltage of −0.076 ± 0.019V, making them well-suited to application in direct-coupled FET logic (DCFL) circuits.