We studied the doping characteristics of Si into molecular‐beam epitaxially grown InAlAs layers for various growth conditions. The growth temperature and V/III beam flux ratio proved to play different roles in Si doping. The growth temperature affects the Si doping concentration, and the V/III flux ratio does the compensation ratio. AtTs=560 °C, a rather high temperature for the growth of InAlAs layers, the Si doping concentration reached 150% as compared with growth atTs=500 °C. With increasing V/III flux ratio, on the other hand, electron mobility and donor concentration increased, suggesting a decreased compensation ratio. We also found a considerable number of electron trapping centers at a low‐growth temperature of 400 °C.