The microfabrication of silicon V-grooves allows to obtain very good positioning accuracies, it is therefore often used for precise alignment of optical fibers. In many cases, it is necessary to etch at the same time V-grooves with variable widths, or V-grooves crossing eachother. In such commonly encountered case, well-known overetching effects appear, leading to structures that are quite uncontrolled in size and depth. Corner compensation methods can reduce such effects to some extent, in some cases. In this report, we present another method which can be used to minimize convex angels overetching. This method can be used alone or in addition to classical corner compensation methods. In some cases, it could even be used when such methods are not possible. We first present the convex angle overetching, and derive the relation between underetching and etching depth. The method relies on discontinuities of the mask, which allow to keep a precise etching geometry until the discontinuity is underetched: the beginning of the corner underetching is thus delayed while the wanted structure is etched with a high accuracy. The control of the underetching rate is obtained through a precise alignment between the mask edges and the crystal orientation. The experiments show that our method allows to reduce significantly the overetching of convex angles. This method is useful to improve or simplify the fabrication of several kinds of microstructures for MEMS or MOEMS applications. We show how it makes feasible a microstructure which mixes closely spaced V-grooves and metal interconnection lines, and how it can improve the fabrication of crossing microchannels.