SiN,AnPIInGaAs doped channel passivated heterojunction insulated gate field effect transistors (HIGFET's) have been fabricated for the first time using an improved In-S interface control layer (ICL). The insulated gate HIGFET's exhibit very low gate leakage (10 nA @ VGS = k5 V) and I~s ( s a t ) of 250 mA/mm. The doped channel improves the DC characteristics and the HIGFET's show transconductance of 140-150 m S / m ( L , = 2 pm), f t of 5-6 GHz ( L , = 3 pm), and power gain of 14.2 dB at 3 GHz. The ICL HIGFET technology is promising for high frequency applications.