We consider a semilinear elliptic boundary value problem with Dirichlet boundary condition $Au+bu^+-au^-=t_{1{phi}1}+t_{2{phi}2}$ in ${Omega}$ and ${phi}_n$ is the eigenfuction corresponding to ${lambda}_n(n=1,2,{cdots})$. We have a concern with the multiplicity of solutions of the equation when ${lambda}_1$ < a < ${lambda}_2$ < b < ${lambda}_3$.