We simulated a Single Electron Tunnel (SET) Transistor with the full inclusion of inelastic macroscopic quantum tunneling of charge (q-MQT) or co-tunneling. Numerical results of the q-MQT effect over a wide range of bias and gate voltage were achieved.Monte Carlo method was used to simulate electrons that tunnel back and forth through the two tunnel junctions of the SET transistor and co-tunnel back and forth through both junctions simultaneously.Resonances in the I-V characteristic were found. The resonant peaks decrease with increasing temperature. The origin of this resonance is the q-MQT or co-tunnel effect in contrast with the normal resonant tunneling in double barriers.