A SiGe bulk crystal with uniform composition was successfully fabricated by clarifying and controlling the growth parameters at the crystal-melt interface. An apparatus was developed for the direct in situ observation and precise control of the interface parameters such as the temperature and the position. The dynamical change of the growth rate of a SiGe bulk crystal in a temperature gradient can be known by utilizing the apparatus. The growing crystal was continuously pulled down at the pulling rate balanced to the growth rate to keep the interface temperature constant, which resulted in the excellent uniformity of the grown crystal. Our technique opened the possibility to incorporate multicomponent semiconductor substrates to the semiconductor heterostructure technology.