  In this paper we are considering a semilinear singular perturbation reaction
-- diffusion boundary value problem, which contains a small perturbation
parameter that acts on the highest order derivative. We construct a difference
scheme on an arbitrary nonequidistant mesh using a collocation method and
Green's function. We show that the constructed difference scheme has a unique
solution and that the scheme is stable. The central result of the paper is
$\epsilon$-uniform convergence of almost second order for the discrete
approximate solution on a modified Shishkin mesh. We finally provide two
numerical examples which illustrate the theoretical results on the uniform
accuracy of the discrete problem, as well as the robustness of the method.
