109.5°.
VESPR helps predict the bond angles with the electrons being the most out. By looking that the structure of the molecule, one Si and four H, the Si atom can be seen as the center and the four H atoms can be seen around it. Now think about how the H atoms would be placed, ideally they would be placed the farthest distance from each other equidistant. So in this case it would be 109.5°.
