We investigate the effects of the shape and orientation of mask openings on selective liquid-phase epitaxial growth of GaAs microtips. Five kinds of mask openings have been designed for this study. First one is a square opening with the four sides parallel to the < 110 > directions. The second is also a square opening, but with the four sides parallel to the < 10 0 > directions, namely the directions having an anale of 45 degrees relative to the < 110 > directions. The third is an equilateral triangle opening with one side parallel to [110] direction. The fourth is a rectangular opening with the four sides parallel to the < 110 > directions. The last one is a round opening. Scanning electron microscopy (SEM) is employed to characterize the GaAs microtips. The results indicate that the pyramidal microtips bounded by four {111} planes are always formed tinder all of the five situations, and the shapes of the microtip tops are either pointed or edged. This means that the 2rowth of the microtip is independent of the shape and orientation of the mask openings. But the ratio of the two maximum sizes of an opening along the [110] and [1 (1) over bar0] directions dominates the top shape of a microtip. A preliminary explanation is also given in this paper. (c) 2007 Elsevier B.V. All rights reserved.