We report on the fabrication and the characterization of low‐loss, single‐mode GaAs/AlGaAs single heterostructure ridge waveguides and a linear electro‐optic phase modulator on silicon substrate. The waveguides and the phase modulator were grown by molecular beam epitaxy and were characterized at a 1.3 &mgr;m wavelength. The average TE mode propagation loss of 1.24 dB/cm, obtained for a 6‐&mgr;m‐wide ridge waveguide, is the lowest loss so far reported. The measured phase shift efficiency of the phase modulator was 3.5°/V mm.