The electrical properties of silicon and beryllium doped (AlyGa1-y)0.52In0.48P grown by gas source molecular beam epitaxy were studied. Unintentionally doped (GaIn)P has a n-type background concentration of 5.1×1014 cm-3 and a free-carrier mobility of ∼3500 cm2/V s at room temperature. Hall measurements of n-(GaIn)P give a linear increase in the free-carrier concentration for values up to 4.0×1018 cm-3. Silicon doping of (GaIn)P and (Al0.7Ga0.3)0.52In0.48P reveals a linear increase in the impurity carrier concentration for values up to 8.0×1018 cm-3 by capacitance–voltage measurements. In contrast, the free electron concentration saturates at a value of 4.8×1017 cm-3 in (Al0.7Ga0.3)0.52In0.48P, due to Fermi-level pinning at the DX level. Beryllium doping of (GaIn)P reveals a linear increase in the Hall free-hole concentration for values up to 1.4×1019 cm-3 with a r- oom-temperature mobility of ∼34 cm2/V s. © 1997 American Institute of Physics.