Chapter 22 - Gauss's Law - Problems - Exercises - Page 745: 22.5

$ \Phi_E = \pi r^{2} E$

The electric field is the same at the center of the hemisphere and any circle. So, the electric flux for the hemisphere will not differ for the sphere and is given by \begin{equation} \Phi_{E}=E A=E\left(\pi r^{2}\right)=\pi r^{2} E \end{equation}