We calculated the unstrained and the strained band structures of InAs and carried out Monte Carlo simulation of InGaAs/strained-InAs/InGaAs composite channel high electron mobility transistors (HEMTs) considering 2-dimensional electron gas (2DEG) self-consistent analysis by solving Schrödinger and Poisson equations. With considering the effect of 2DEG, the drain-source current Ids decreases. However, the negative threshold voltage shift due to the short-channel effects is not affected by considering 2DEG. The threshold voltage shift occurs in the region Lg/d < ∼5 (Lg: gate length, d: sum of the barrier and channel layer thicknesses). At Lg = 20 nm, the simulated cutoff frequency ƒT values were 943 GHz without 2DEG and 813 GHz with 2DEG. The trend of the ƒT values with Lg reflects that of the electron velocities mainly.