Enter the thermal voltage, the depletion layer capacitance, and the gate-oxide capacitance into the Subthreshold Swing Calculator. The calculator will evaluate the Subthreshold Swing. 

Subthreshold Swing Formula

The following formula is used to calculate the Subthreshold Swing. 

Ss = ln(10) * kt/q * (1 + Cd/Cox)


  • Ss is the Subthreshold Swing ( )
  • kt/q is the thermal voltage 
  • Cd is the depletion layer capacitance 
  • Cox is the gate-oxide capacitance 

How to Calculate Subthreshold Swing?

The following steps outline how to calculate the Subthreshold Swing.

  1. First, determine the thermal voltage.
  2. Next, determine the depletion layer capacitance. 
  3. Next, determine the gate-oxide capacitance. 
  4. Next, gather the formula from above = Ss = ln(10) * kt/q * (1 + Cd/Cox).
  5. Finally, calculate the Subthreshold Swing.
  6. After inserting the variables and calculating the result, check your answer with the calculator above. 

Example Problem:

Use the following variables as an example problem to test your knowledge.

thermal voltage = 30

depletion layer capacitance = 14

gate-oxide capacitance = 30

Ss = ln(10) * kt/q * (1 + Cd/Cox) =  ?