High temperature dimensional reduction of the MSSM and other multiscalar models in the [Formula presented] limit

Using dimensional reduction we construct an effective 3D theory of the minimal supersymmetric standard model in the [Formula presented] limit at finite temperature. The final effective theory is obtained after three successive stages of integration out of massive particles. We obtain the full one-loop relation between the couplings of the reduced theory and the underlying 4D couplings and masses. The procedure is also applied to a general two Higgs doublet model and the next to minimal supersymmetric standard model.