temperature of the substrate is in the range of 300 u00b0 to 700 u00b0 c the monocrystal of gaas may be subjected to the epitaxial growth the electric characteristics of the obtained film were that the growth temperature was in the neighborhood of 550 u00b0 to 600 u00b0 c the density of impurity 5 u00d7 10 15 cm 3 and the mobility 35 000 cm 2 v 1 s 1 77 u00b0 k or more when the growth pressure within the reaction pipe is varied with the flow rate of gas set to be constant the growth speed slowly decreases together with pressure in the atmospheric pressure of 0 2 to 0 001 but the quality of film increases while in the above described embodiment a description has been made by use of a resistance heating electric furnace it is to be of course noted that an infrared ray heating furnace may be used for the growth of crystal furthermore while in the aforementioned embodiment an example has been illustrated to use a heating electric furnace for cracking gacl 3 it is to be noted that instead light radiation may he used to crack gacl 3 fig4 shows an example in which light radiation is superimposed to heating by an electric furnace in which parts corresponding to those shown in the embodiment of fig1 are indicated by the same reference numerals as those used previously reference numerals 41 and 42 designate window members through which ultraviolet radiation travels which are.