We address the topology of the set of singularities of a solution of a Hamilton-Jacobi equation. For this we will apply the idea of the first two authors (Generalized characteristic and Lax-Oleinik operators: global result, preprint, arXiv:1605.07581, 2016.) to use the positive Lax-Oleinik semi-group to propagate singularities. {\it To cite this article: P. Cannarsa, W. Cheng, A. Fathi, C. R. Acad. Sci. Paris, Ser. I 340 (2005).