We study the semi-classical ground states of the nonlinear MaxwellDirac system with critical/subcritical nonlinearities:for x ∈ R 3 , where A = (A 1 , A 2 , A 3 ) is the magnetic field, φ is the electron field, q is the changing pointwise charge distribution. We develop a variational argument to establish the existence of least energy solutions for small. We also describe the concentration phenomena of the solutions as → 0.Mathematics Subject Classifications (2000): 35Q40, 49J35.