We have grown high‐quality In0.48Ga0.52P layers on GaAs(001) substrates using solid‐source molecular‐beam epitaxy. A dimer phosphorous (P2) molecular beam was produced from a GaP decomposition source. The full width at half‐maximum of the (004) double‐crystal x‐ray diffraction peak from a 1.7‐μm‐thick InGaP layer on GaAs(001) substrate was 16 arcsec, which is comparable with the smallest values ever reported. The photoluminescence linewidth at 10 K is 16 meV. Hall measurements are carried out on undoped, Si‐doped, and Be‐doped InGaP layers grown with a 2×1 surface reconstruction. The electron mobilities are comparable to similar InGaP/GaAs layers grown by gas‐source molecular‐beam epitaxy. Undoped InGaP layers grown with a 2×2 reconstruction, however, showed a high resistivity of ≥102 Ω cm at 300 K.