  Temperature dependence of the upper critical field $H_{c2}$ of the Dirac semi
- metal (DSM) with phonon mediated pairing is considered within semi -
classical approximation. The low temperature dependence deviates from
conventional BCS superconductor with parabolic dispersion relation\cite{WHH}
even for large adiabaticity parameter, $\gamma =\mu /\left( \hbar \Omega
\right) $., where $\mu $ is the chemical potential and $\Omega $ - Debye
frequency. In particular the "reduced field", ratio of zero temperature $%
H_{c2}$ to derivative at critical temperature, $h^{\ast }=H_{c2}\left( 0\right)
/\left( -T\frac{dH_{c2}}{dT}\right) |_{T_{c}}$, depends on $\gamma $ and can be
extended beyond the adiabatic limit. The reduced magnetic field ratio is
universal (independent of the chemical potential, interaction strength etc.)
and smaller than the Werthamer ratio for clean superconductors: $h^{\ast
}=0.55$ for DSM, $h^{\ast }\left( 0\right) =0.69$ for parabolic band. The
results are in good agreement compared with recent experiments on $TaP$.
