GaAs and AlGaAs were deposited on silicon for the first time using conformal MOVPE growth, a lateral epitaxial overgrowth technique. Since this method requires selective growth, the chlorine-containing precursors dimethylgalliumchloride (DMGaCl) and dimethylaluminumchloride (DMAlCl) were used to prevent polycrystalline nucleations on the dielectric mask and the silicon substrate. The vapor pressures of these precursors have been determined. Several precursors for doping (hydrogen sulfide (H2S), diethylzinc (DEZn), carbontetrabromide (CBr4)) were tested together with the chlorine-containing precursors. Microphotoluminescence (mu -PL) and cathodoluminescence (CL) measurements were carried out on the conformal (Al)GaAs structures to determine the extension of the conformal layers. SEM pictures reveal the shape of the growth front.