Recently, multiple quantum wells structure are often used in the laser and diode applications in order to increase their efficiency. In this structure,electron tunnelling phenomena from a quantum well to another well play a key role in electronic transport itself. Tunnelling is a quantum mechanical phenemenon where an electron is commonly represented by its wavefunction. This paper presents a numerical simulation of electron tunnelling probality on tree quantum wels (quadruple barrier) Si/SiO2 system focusting the applied bias effect on the tunnelling probability. The tunnelling probabilty is calculated by solving the Schrodinger's equations through potential barrier using transfer matrix method. The simulation results show the ,ini-band formation due to the apperance of discrete energy group. We also found that the applied bias on this structure causes the changes in tunnelling probability and discrete energy gap. Therefore, the control of voltage bias and device structure is required in order to obtain expected characteristic of multiple quantum well structure.