0.1% B2H6diluted in hydrogen is used as thep‐type dopant gas in Si1−xGexgrown by ultrahigh vacuum chemical vapor deposition (UHVCVD) using Si2H6and GeH4. The boron concentration is evaluated by secondary ion mass spectrometry (SIMS). The boron concentration of Si1−xGexincreases with the increase of the GeH4flow rate, that is, Ge fraction, by keeping Si2H6and B2H6flow rates constant. The result may be due to the increase of the vacant surface sites which is caused by the increase of the hydrogen desorption rate when a higher Ge fraction epilayer is grown. ©1995 American Institute of Physics.