  It is shown that supersymmetry is spontaneously broken in certain
three-dimensional supersymmetric gauge theories, by using the s-rule in their
string theory realization as brane configurations. In particular, supersymmetry
is broken in N=3 supersymmetric Yang-Mills-Chern-Simons theory with gauge group
SU(n) and CS coefficient k, as well as in its N=2 and N=1 deformations, when
n>|k|. In addition, supersymmetry is broken in the N=1 mass deformation of N=2
supersymmetric Yang-Mills theory with gauge group SU(n) and one matter
multiplet when n>1. In the latter case the breaking is induced by an
instanton-generated repulsive potential.
