Aluminium lines have been deposited on semi-insulating gallium arsenide (100) substrates by visible Ar+ laser decomposition of trimethylamine alane. The aluminium resistivity, measured by a two-point test method, has been found to be as low as 6 muOMEGA cm. A grating composed of parallel aluminium lines (20 mum wide, 1000 angstrom thick and spaced 35 mum apart) was written directly with a laser power of 0.8 W and a scanning speed of 50 mum s-1. The induced temperature at the centre of the laser spot was estimated at about 350-degrees-C. A similar grating was evaporated in a ultra-high vacuum chamber equipped with an electron gun. Prior to deposition of these two gratings, an aluminium back contact was evaporated on both substrates. In order to compare the electrical quality of the Al/GaAs interfaces obtained by both deposition processes, the current--voltage characteristics as a function of temperature, as well as the photocurrent intensity delivered by the samples under illumination as a function of bias and photon energy, have been measured. The results show that laser deposition can be used to perform a full metallization level (few meter connections) comparable in quality with conventional ultra-high vacuum evaporated deposits.