The dissociation of excitons into holes and electrons in photoexcited semiconductors, despite being one of the first recognized examples of a Mott transition, still defies a complete understanding, especially regarding the character of the transition, which is first order in some cases and second order in others. Here we consider an idealized model of photoexcited semiconductors that can be mapped onto a spin-polarised half-filled Hubbard model, whose phase diagram reproduces most of the phenomenology of photoexcited semiconductors and uncovers the key role of the exciton binding energy in determining the order of the exciton Mott transition