*Not to be confused with Oxide Thickness (t*_{OX}).

**Equivalent Oxide Thickness** (**EOT**), represented by `t`

or _{eq}`t`

, is the gate oxide thickness of the SiO_{OXE}_{2} layer of a transistor that would be required to achieve similar capacitance density as the high-κ material used.

A gate dielectric with a dielectric constant that is substantially higher than that of SiO_{2} will initially have a much smaller equivalent electrical thickness. This key feature allowed for the industry to continue on with Moore's Law. As the semiconductor industry began to experiment with transitioning from a SiO_{2} gate oxide to a high-κ material, EOT can be used to quickly compare those materials using existing SiO_{2}-based models.

## Equation

One can treat MOSFET behavior like two parallel plate capacitors,

Where is the relative dielectric constant of SiO_{2} in our case. Therefore one calculate the equivalent oxide thickness as,

Note that the dielectric constant SiO_{2} is 3.9

Where `t`

is the equivalent oxide thickness, _{oxe}`ε`

is the dielectric constant of the high-κ material used, and _{high-κ}`t`

is the physical oxide layer thickness.
_{ox}

## Example

For example, consider Hafnium Dioxide (HfO_{2}) which has an (subject to variations in temperature). A layer of just 1 nm in thickness would result in an equivalent oxide thickness of around . This is indeed the material used by Intel following their transition to high-κ at the 45 nm process node.