We report on self-consistent field predictions for the formation of spherical micelles by A(N)B(M)C(N) triblock terpolymers in a selective solvent, that is, a good solvent for the A(N) and C-N blocks and a poor solvent for the middle B-M block. Above some threshold value for the repulsion between the A and C monomers, we find micelles with a laterally segregated corona, that is, Janus micelles. We consider the thermodynamic stability, the size, and the size fluctuations of these micelles. The transition between the homogeneous and the segregated states is smooth not only because of the finite size of the system, but also due to the compositional symmetry within the triblock terpolymer. It is found that the aggregation number decreases with increasing repulsion between A and C below the transition point and increases above the transition point. The formation of the interface is triggered by the high polymer density near the core. The interface between the A and C rich regions occupies a constant angle in spherical coordinates. This means that it widens in the radial direction. In these micelles, the lateral segregation gives a new fluctuation mode to the micelles; as the lateral segregation is coupled to the aggregation number, we anticipate a rich behavior in experimental systems.