  We theoretically investigate ferromagnetic ordering in magnetically doped
solid-solution narrow-gap semiconductors with the strong spin-orbit interaction
such as Cr-doped Bi$_2$(Se$_x$Te$_{1-x}$)$_3$. We compute the spontaneous
magnetization of impurities and itinerant electrons, and estimate the critical
temperature as a function of the concentration of magnetic dopants and the
strength of the spin-orbit interaction. It is found that the critical
temperature is proportional to the concentration of dopants and enhanced with
the strong spin-orbit interaction. It is also found that the ferromagnetic
transition could make the system turn to the Weyl semimetal which possesses a
pair of Weyl points separating in the momentum space.
