We study a lattice model of interacting Dirac fermions in (2 + 1) dimension space-time with an SU(4) symmetry. While increasing interaction strength, this model undergoes a continuous quantum phase transition from the weakly interacting Dirac semimetal to a fully gapped and nondegenerate phase without condensing any Dirac fermion bilinear mass operator. This unusual mechanism for mass generation is consistent with recent studies of interacting topological insulators/superconductors, and also consistent with recent progresses in lattice QCD community. Introduction. In the Standard Model of particle physics, all the matter fields, quarks and leptons, acquire their mass from "spontaneous symmetry breaking", or equivalently the condensation of the Higgs field [1-3]. The Higgs field couples to the bilinear mass operator of the Dirac fermion matter fields (except for the neutrinos), and hence the matters acquire a mass in the condensate. In the context of correlated electron systems, mass generation (or gap opening) due to interaction is also often a consequence of spontaneous symmetry breaking and the development of certain long-range order. For example, in a superconductor the Cooper pairs condense, which spontaneously breaks the U (1) charge symmetry of the electrons, and as a result the electrons acquire a mass gap at the Fermi surface. So, consensus has that, in strongly interacting fermionic systems (either in condensed matter or high energy physics), mass (or gap) generation is usually related to spontaneous symmetry breaking and the condensation of a fermion bilinear operator [4].