In this paper it is shown that tunneling probability of electrons (TP), capacitance equivalent oxide thickness (CET), and propagation delay time (τpd) of high-k MISFETs are strongly affected by interfacial layer (IL) materials in the case that wave function penetration into gate dielectrics is taken into consideration. Using reported barrier heights and effective masses, these parameters in MISFETs with HfO2/IL stacked gate dielectrics with interfacial layer of SiO2, Si3N4, Al2O3, Ta2O5, and SrTiO3 are quantitatively studied.