This paper focuses on electron traps in HfO2/SiO2 stacks. Three issues are addressed: the impact of measurement techniques on trapping, the dependence of trapping on the conduction mechanism, and the trapping kinetics. It will be shown that the traditional 'DC Id similar to Vg' technique can underestimate the trap density. Trapping is sensitive to the conduction mechanism. The trap-assisted conduction, such as SILC and thermally enhanced conduction, contributes little to the trapping. Possible explanations for this phenomenon will be explored. Trapping follows the first order model and the capture cross section of traps is estimated.