Second order sufficient optimality conditions are considered for a simplified class of semilinear parabolic equations with quadratic objective functional including distributed and terminal observation. Main emphasis is laid on problems where the objective functional does not include a Tikhonov regularization term. Here, standard second order conditions cannot be expected to hold. For this case, new second order conditions are established that are based on different types of critical cone. Depending on the choice of this cone, the second order conditions are sufficient for local minima that are weak or strong in the sense of calculus of variations.