Mass action law (electronics)

In electronics and semiconductor physics, the law of mass action relates the concentrations of free electrons and electron holes under thermal equilibrium. It states that, under thermal equilibrium, the product of the free electron concentration ${\displaystyle n}$ and the free hole concentration ${\displaystyle p}$ is equal to a constant square of intrinsic carrier concentration ${\displaystyle n_{\text{i}}}$. The intrinsic carrier concentration is a function of temperature.

The equation for the mass action law for semiconductors is:^[1] $${\displaystyle np=n_{\text{i}}^{2}}$$