The Hamiltonian approach to the problem of tunneling of relativistic partic
les has been developed. The method is described by applying it to a specifi
c example, the theory of the ionization of a relativistic bound state (whos
e binding energy is comparable with the electron rest energy mc(2)) under t
he effect of external electric and magnetic fields. It has been shown that
the Hamiltonian approach makes it possible to obtain an explicit expression
for both exponential and preexponential factors in the ionization probabil
ity.