Several possible gravitational wave production schemes in the early Universe have been studied before, like bosonic preheating and phase transitions. We will introduce for the first time the spectrum of gravitational waves produced by fermions. Preheating and other particle production phenomena in the early Universe can give rise to high-energy out-of-equilibrium fermions. These fermions develop a source for gravitational waves, an anisotropic stress. We will present a formalism to regularize the source and to calculate the spectrum of gravitational waves from this process.