The conditions, i.e., the interparticle potentials, for which vapor–liquid coexistence is supplanted by microphase separation are examined. The liquid phase is found for potentials with a steeply repulsive core and an attraction of not-too-short a range. To this potential we add a repulsion of longer range than the attraction and find that it breaks up and mixes coexisting bulk vapor and liquid to form a single microphase-separated phase. Our spherical particles are perhaps the simplest continuum model to show a Lifshitz point and microphase separation. In the microphase-separated phase the density is modulated with a period typically ten times the size of the particle’s core. Microphase separation, apart from providing a rich and interesting phase behavior, may have a potential use in nanoelectronic applications.