In this paper we consider the three-dimensional Schrödinger operator with a δ-interaction of strength α > 0 supported on an unbounded surface parametrized by the mappingThe surface supporting the interaction can be viewed as a local deformation of the plane. It is known that the essential spectrum of this Schrödinger operator coincides with [− 1 4 α 2 , +∞). We prove that for all sufficiently small β > 0 its discrete spectrum is non-empty and consists of a unique simple eigenvalue. Moreover, we obtain an asymptotic expansion of this eigenvalue in the limit β → 0+. In particular, this eigenvalue tends to − 1 4 α 2 exponentially fast as β → 0+.2010 Mathematics Subject Classification. 35P15 (primary); 58J50, 81Q37 (secondary). Key words and phrases. Singular Schrödinger operator, δ-interaction on a locally deformed plane, existence of bound states, asymptotics of the bound state, small deformation limit, Birman-Schwinger principle.