A new analytical threshold voltage model for InAlAs/InGaAs heterostructure, InP based HEMT has been developed considering the short-channel effect in subthreshold regime. The model is developed following the MESFET analysis, considering fully depleted InAlAs region as two isolated depletions-one due to metal-semiconductor contact and other due to transfer of carriers from InAlAs region to the 2DEG quantum well. Poisson's equation is solved using Green's Function technique and the solution is then verified by comparing it with Numerical technique. The 2D threshold voltage obtained from our analysis was found to be in good agreement with I D threshold voltage for higher gate lengths, thus proving the validity of our model. (C) 2003 Elsevier Ltd. All rights reserved.