Spontaneous CP Violation in the Minimal Supersymmetric Standard Model at Finite Temperature

We show that in the Minimal Supersymmetric Standard Model one--loop effects at finite temperature may lead to a spontaneous breaking of CP invariance in the scalar sector. Requiring that the breaking takes place at the critical temperature for the electroweak phase transition, we find that the parameters space is compatible with a mass of the Higgs pseudoscalar in agreement with the present experimental lower bounds. Possible implications for baryogenesis are discussed.