In 4H-SiC, 3C stacking fault (SF) behaves like a finite thickness type U quantum well. As a consequence, it can bind two excitons per well. We show in this work that, as the SF thickness increases, the relative intensity of the two transitions changes. This comes from a change in the wave functions overlap between the electron trapped in the well and the holes trapped neighbouring parts of the 4H-SiC matrix.