We report on a recent computation of the
form factors in semi-leptonic decays of the $\mathrm{B}_\mathrm{s}$
using Heavy Quark Effective Theory (HQET) formalism
applied on the lattice. The connection of the form factors
with the 2-point and 3-point correlators on the lattice is
explained, and the subsequent non-perturbative renormalization
of HQET and it's matching to $N_f=2$ QCD is outlined. The
results of the (static) leading-order calculation in the
continuum limit is presented.
