We utilize the sensitivity of the two‐ to three‐dimensional growth transition of InAs self‐assembled islands on InAs coverage to demonstrate the growth of self‐aligned InAs islands on etchedGaAs ridges by molecular beam epitaxy. The different migration behavior of In adatoms on different crystal planes of etched ridges is used to spatially modulate the supply of In adatoms. The ridges are oriented either along the [011] and [011̄] direction on (100) substrates with grating spacing of 0.28, 1, and 5 μm. Atomic force microscopy reveals that the InAs islands are self‐aligned along the ridges and they have a typical size of 400 Å in diameter and 120 Å in height. In samples with [011] oriented ridges, the islands are located on the sidewalls. On the other hand, for [011̄] oriented ridges the islands are on the (100) planes on and at the foot of the mesa. On samples with a grating pitch of 0.28 μm, all the islands are located either on the sidewalls or at the bottom of the ‘‘V groove’’ for both grating orientations.