In this paper, we describe the application of the low angle incidence microchannel epitaxy (LAIMCE) to the epitaxial growth of GaAs on GaAs(001) substrates patterned with a SiO2 mask. By LAIMCE, the selective area growth (SAG) and enhancement of lateral growth on the mask can be achieved in molecular beam epitaxy. At a substrate temperature of 610 degrees C and a beam equivalent growth rate of 1.0 mu m/h, we were able to grow smooth epilayers laterally on the mask. We have studied the dependence of the maximum top width of the epilayers on the angle between the Ga flux and the direction of the GaAs line seed. It was found that the crystallographic orientation has a strong influence on the width of the epilayers and that the width has relative minimums corresponding to the low index crystallographic directions. We have found that the morphology of the epilayers depends also on the mask width between adjacent windows. Moreover, we have studied the coalescence of epilayers growing from adjacent windows and we have found the formation of spiral mono-atomic steps on the coalescence line as a consequence of thr appearance of screw dislocations.