In this paper we investigate the smallest eigenvalue, denoted as λ N , of a (N +1)×(N +1) Hankel or moments matrix, associated with the weight, w(x) = exp(−x β ), x > 0, β > 0, in the large N limit. Using a previous result, the asymptotics for the polynomials, P n (z), z / ∈ [0, ∞), orthonormal with respect to w, which are required in the determination of λ N are found. Adopting an argument of Szegö the asymptotic behaviour of λ N , for β > 1/2 where the related moment problem is determinate, is derived. This generalises the result given by Szegö for β = 1. It is shown that for β > 1/2 the smallest eigenvalue of the infinite Hankel matrix is zero, while for 0 < β < 1/2 it is greater then a positive constant. This shows a phase transition in the corresponding Hermitian random matrix model as the parameter β varies with β = 1/2 identified as the critical point. The smallest eigenvalue at this point is conjectured.