AbstractThe electron transport phenomena in InGaAs HEMTs at low Vgs condition are shown to be similar to Si MOSFETs. At the potential bottleneck under the gate, the momentum distribution function of the electron, f (x, kx), becomes an asymmetric shape with a small tail spread in negative direction. As Lg decreases, the negative tail of f (x, kx) becomes less significant, which is responsible for the increase of the electron velocity at the bottleneck, vs. We demonstrate that the electron scatterings collapse the hemispherical shape of f (x, kx) at the bottleneck. As Lg decreases, vs approaches the ballistic value. The ballisticity is estimated on the basis of the quasi‐ballistic transport theory. The backscattering coefficient, R, decreases and the index of the ballisticity, rB, increases as Lg decreases. At Lg = 10 nm, R and rB are estimated to be about 0.05 and 0.97, respectively, which indicates that at Lg = 10 nm, vs is almost reaching the ballistic limit. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)