We have studied relativistic effects on the tunnelling of electrons th
rough a multi-barrier system (MBS) consisting of rectangular barrier p
otentials, by deriving, for the purpose, relativistic formulae for the
transmission coefficient and associated relativistic conditions for r
esonant tunnelling. Among other things, we have discussed critically t
he quantitative extents of relativistic impacts on tunnelling through
MBSS, especially in the context of their measurability.