%0 Journal Article %T A Note on Formality and Singularities of Moduli Spaces %A Ziyu Zhang %J Mathematics %D 2010 %I arXiv %X This paper studies formality of the differential graded algebra $RHom(E,E)$, where $E$ is a semistable sheaf on a K3 surface. The main tool is Kaledin's theorem on formality in families. For a large class of sheaves $E$, this DG algebra is formal, therefore we have an explicit description of the singularity type of the moduli space of semistable sheaves at the point represented by $E$. This paper also explains why Kaledin's theorem fails to apply in the remaining case. %U http://arxiv.org/abs/1011.4689v1