Si-doped InAsxP1-x layers with As mole fractions ranging from 0.05 to 0.50 were grown on InAsxP1-x step-graded buffer layers on InP substrates by solid source molecular beam epitaxy. The growth parameters consisted of a P:In flux ratio of 7:1, a growth temperature of ∼ 485°C, a growth rate of 2.2 Å/s, and an As:In flux ratio of 0.37-2.36 for varying As mole fractions. The As mole fraction and the layer relaxation were determined using triple axis x-ray diffraction measurements. Near complete relaxation (>93%) was achieved for all Si-doped InAsxP1-x epilayers. The structural morphology indicated that the InAsxP1-x graded buffer layers were effective in relieving the lattice mismatch strain as evidenced by a well-developed crosshatch morphology and low rms surface roughness. The electron concentration, mobility, and Si donor activation energy for each InAsxP1-x composition were determined using temperature dependent Hall measurements. At a constant electron carrier concentration of %3.5×1016 cm-3, the 300 K carrier mobility increased from 2700 to 4732 cm2/V-sec with increasing As mole fraction from 0.05 to 0.50.