We present a novel scheme for performing a conditional phase gate between two spin qubits in adjacent semiconductor quantum dots through delocalized single exciton states, formed through the interdot Fo貳ter interaction. We consider two resonant quantum dots, each containing a single excess conduction band electron whose spin embodies the qubit.We demonstrate that both the two-qubit gate and arbitrary single-qubit rotations may be realized to a high fidelity with current semiconductor and laser technology.