Аннотация:In the framework of the two-Higgs-doublet model with temperature-dependent effective parameters $\lambda_{1,...7}(T)$ we define the four bifurcation sets which appear as a consequence of the condition ${\tt det} \partial^2 U_{ij}/ \partial v_i \partial v_j =$0 for the stability matrix. Numerical investigations of the electroweak phase transition are performed for the full MSSM parameter space ($m_{H^\pm}$, ${\tt tg}\beta$, $A_{t,b}$,
$\mu$, $m_Q$, $m_U$, $m_D$) using the temperature-dependent effective parameters $\lambda_1$-$\lambda_5(T)$ calculated at the one-loop in the imaginary time formalism. Four types of transitions can take place in the MSSM background field space ($v_1$, $v_2$). They are different in the direction, defined by a critical angle in the ($v_1$, $v_2$) plane, and in the strength, which is estimated by means of Shaposhnikov criteria $v_c/T_c >$1. Extensive regions in the ($A_{t,b}$, $\mu$) plane correspond to the strongly first order phase transition. The case of light top quark superpartner is favored, giving an acceptable configurations of surfaces for extrema of the effective potential.