The mechanisms of molecular beam epitaxy growth on the mesa patterned substrates which results in the formation of sharp ridge structure were investigated. A simple model, based oil the scanning electron microscope measurements, nicely explains the time dependent growth rates as well as the change of the facet shape during the formation of ridge structure originating from the strong Ga atoms migration. The estimated number of atoms crossing the boundary changes according to the alternating facet shape and this indicates the instability in the facet growth. As a result, the mechanism of mesa growth was clarified, which becomes self-regulatory while the facet shape and/or the boundary condition vary as the growth progresses.