Self-assembled monolayers with low molecular surface density of decanethiol on Au(lll) have been prepared by annealing of the densely packed (root 3 x root 3)R30 degrees structure. High-resolution scanning tunneling microscope (STM) imaging reveals the formation of a 11.5 x root 3 stripe structure where the molecules are aligned along the substrate surface in double lamellae. We can deduce from the images that the molecules bind to specific sites at the Au(lll) surface rather than adsorb as didecane disulfides. For the first time, a lattice structure for an alkanethiol stripe phase can be derived from the obtained real-space data.