where Vtn is the threshold voltage at zero body bias, γ is the body effect coefficient, φf is the Fermi potential, and Vsb is the source-body voltage.
Substituting typical values:
The intrinsic carrier concentration in silicon at 300 K can be calculated using the following equation: Advanced Semiconductor Fundamentals Solution Manual
4.1 Calculate the threshold voltage of a MOSFET. where Vtn is the threshold voltage at zero
Vbi = (kT/q) * ln(Na * Nd / ni^2)