  We study the implications of a light stop for the spontaneous CP breaking at
finite temperature in the Higgs sector of the Minimal Supersymmetric Standard
Model with a gauge singlet. Assuming CP conservation at zero temperature, we
show that the presence of a large mixing between the left- and the right-handed
stops can trigger easily the spontaneous breaking of CP inside the bubbles
nucleated during the electroweak phase transition. This allows to avoid the
fine-tuning among the vacuum expectation values in the region of interest for
the generation of the baryon asymmetry, namely the bubble walls, which has been
recently analized.
