A direct comparative study of the interfaces AL/H:Si(111)-(1x1) and Al/Si(111)-(7x7) by means of high-resolution photoelectron spectroscopy and Auger spectroscopy reveals large differences for aluminum coverages below Theta-5 ML. Hydrogen termination suppresses the formation of interfacial AlSi and promotes island growth. The Schottky barrier formation is delayed compared to the Al/Si(111)-(7x7) interface. For high coverages the Schottky barrier is the same for both interfaces.