The mechanical properties and thermal stresses of hydrogen silsesquioxane (HSQ) thin films cured at different temperatures have been investigated by a nanoindentor and a profilometer. In this study, the correlations between structure change, Si-H/Si-O ratio, modulus, hardness, and calculated CTE of HSQ films have been established. The results show that the Si-H/Si-O ratio of HSQ films decreases with increasing curing temperature due to the loss of Si-H bonds when it forms the network structure at higher curing temperatures. In addition, both the modulus and hardness of HSQ films increase with increasing curing temperature. However, the calculated coefficient of thermal expansion (CTE) decreases with increasing curing temperature. These results indicate that the increase in modulus and hardness and the decrease in CTE are due to the conversion of Si-H into Si-O bonds with the reduction in porosity when forming the network structure in the HSQ films at higher cure temperatures.