  We propose an analytical study of relativistic tunneling through opaque
barriers. We obtain a closed formula for the phase time. This formula is in
excellent agreement with the numerical simulations and corrects the standard
formula obtained by the stationary phase method. An important result is found
when the upper limit of the incoming energy distribution coincides with the
upper limit of the tunneling zone. In this case, the phase time is proportional
to the barrier width.
