Plasma phase transitions in dense hydrogen and electron‐hole plasmas are investigated by direct path integral Monte Carlo (DPIMC) method. The results are compared with existing theoretical and experimental data. The phase boundary of the electron‐hole liquid in germanium is calculated in agreement with the known experimental results. High‐density hydrogen exhibits similar behavior. In both cases the phase transition is accompanied by the conductivity rise and the internal energy is lowered due to the formation of droplets. The high‐density part of the deuterium shock Hugoniot is computed using the simulation results. © 2004 American Institute of Physics