A theoretical formulation for the leakage gate current in a heterostructure insulated-gate field effect transistor (HIGFET) is presented. Three important components of the leakage gate current, namely 2-D tunneling, 3-D tunneling and thermionic emission current, are considered. The conduction band edge profile of the HIGFET is obtained by a self consistent solution to the Poisson and Schroedinger equations. The transmission coefficient for 2-D and 3-D tunneling currents is obtained by solving the Schroedinger equation; The leakage gate currents are obtained as a function of the gate voltage for the AlI-nAs/GaInAs and AlGaAs/GaAs based HIGFET structures. For the AlInAs/GaInAs system, the calculated leakage currents are within a factor of 10 of the experimental values for most of the voltage range of study. This is more accurate than the results obtained in earlier literature, where the currents are off by more than a factor of 100 for most of the voltage range. For the AlGaAs/GaAs system, the qualitative behaviour of the results are good, however, the calculated currents are off by about a factor of 1000 for most gate voltages. The reasons for this discrepancy are discussed
