  We discuss the Schwinger pair creation process for the system of massless
Dirac fermions in the presence of constant external magnetic and electric
fields. The pair production rate remains finite unlike the vacuum decay rate.
In the recently discovered Dirac semimetals, where the massless Dirac fermions
emerge, this pair production may be observed experimentally through the
transport properties. We estimate its contribution to the ordinary conductivity
of the semimetals.
