An analysis of the cracking behavior of sol-gel derived silica, "xerogel," films on silicon substrates is presented. At the onset of film cracking, xerogel films on 〈100〉 Si substrates show a crosshatched crack pattern, while such films on 〈111〉 Si substrates show a random pattern. This is explained by the fact that for an isotropic film the critical film thickness for cracking decreases for increasing substrate compliance. For a 〈100〉 Si wafer, the directions of highest compliance in the plane of the wafer are in the 〈100〉 directions, which lead to cracks in the film parallel to them. A 〈111〉 Si substrate is isotropic in the plane of the wafer and, hence, there is no preferred direction for film cracking. A random pattern is the result.