Reduction of unintentional silicon impurity in GaInAs was obtained by using a SiC-coated graphite boat containing Ga-In source alloy materials. A maximum mobility of 2800 cm(2)/(V.s) and a carrier concentration of 1.4 x 10(18) cm(-3) were obtained at room temperature with a quartz boat. The addition of a small amount of dysprosium as a gettering material resulted in reducing the background concentration and also the mobility. However, use of a SiC-coated graphite boat resulted in an increase of the room temperature mobility to 5100 cm(2)/(V.s) and a decrease in carrier concentration to 2.8 X 10(16) cm(-3).