Low- and high-field transports are investigated for HfO 2 -based MOSFETs with ultrathin equivalent oxide thickness (UTEOT) (EOT = 6.4-8.4 Å) achieved by a remote interface layer (IL) scavenging method. A detailed comparison with a SiON reference demonstrates none of the detrimental effects from HfO 2-related Coulomb nor phonon additional scattering on the high-field velocity. Increased surface roughness may reduce the high-field velocity by 20% for the device with the thinnest IL. This is explained by an increase of the backscattering which reduces the ballistic efficiency for the shortest devices (L MET = 25nm). However, the on-state current (I ON) for UTEOT devices has the best performance at a given high-lateral-field velocity. Therefore, EOT scaling remains a valid tool for I ON-performance improvement for CMOS scaling also with new architectures and substrates.