  We consider self-adjoint Dirac operators $\ham{D}=\ham{D}_0 + V(x)$, where
$\ham{D}_0$ is the free three-dimensional Dirac operator and $V(x)$ is a smooth
compactly supported Hermitian matrix. We define resonances of $\ham{D}$ as
poles of the meromorphic continuation of its cut-off resolvent. An upper bound
on the number of resonances in disks, an estimate on the scattering determinant
and the Lifshits-Krein trace formula then leads to a global Poisson wave trace
formula for resonances of $\ham{D}$.
