We consider the nonlinear Sturm–Liouville problem-u″(t)+u(t)p=λu(t), u(t)>0, tI(0, 1), u(0)=u(1)=0, where p>1 is a constant and λ>0 is an eigenvalue parameter. To understand the global structure of the bifurcation diagram in R+×L2(I) completely, we establish the asymptotic expansion of λ(α) (associated with eigenfunction uα with uα2=α) as α→∞. We also obtain the corresponding asymptotics of the width of the boundary layer of uα as α→∞.