Disilane (Si2H6) is presented as a new silicon doping source in the metalorganic chemical vapor deposition of GaAs together with comparison results obtained using the conventional silane (SiH4) doping source. The doping characteristics of disilane were studied over a wide range of growth conditions: temperature, gas phase stoichiometry, and disilane concentration in the growth ambient. Silicon incorporation by means of disilane pyrolysis showed no temperature dependence, in sharp contrast to the strong temperature activated dependence found when employing silane. The decomposition reaction of disilane proved to be very efficient, reducing the amount of dopant gas required by about two orders of magnitude at the lower growth temperatures. Electrical measurements on disilane-doped GaAs yield the same high mobilities as obtained in silane-doped GaAs films, indicative of low compensation.