Splitting methods are powerful numerical schemes which allow us to divide an evolution problem into easier subproblems. For reaction-diffusion equations, the Strang splitting method, which is formally second order accurate, allows us to solve separately the diffusive process and the reaction process. In this context however, the Strang splitting suffers in general from a reduction of order which can drastically reduce its efficiency. This reduction of accuracy occurs because the reaction flow does not preserve the domain boundary conditions in general. In this thesis, we develop and analyze new remedies to avoid the reduction of order of the Strang splitting for semilinear parabolic problems with Dirichlet, Neumann, Robin or absorbing boundary conditions. Numerical experiments illustrate the behavior of these new approaches.