  In this paper we study the Martin boundary of unbounded open sets at infinity
for a large class of subordinate Brownian motions. We first prove that, for
such subordinate Brownian motions, the uniform boundary Harnack principle at
infinity holds for arbitrary unbounded open sets. Then we introduce the notion
of $\kappa$-fatness at infinity for open sets and show that the Martin boundary
at infinity of any such open set consists of exactly one point and that point
is a minimal Martin boundary point.
