<p>The degrees of freedom of Active Flux are cell averages and point values along the cell boundaries. The latter are shared between neighboring cells, which gives rise to a globally continuous reconstruction. The semi-discrete Active Flux method uses its degrees of freedom to obtain Finite Difference approximations to the spatial derivatives which are used in the point value update. The averages are updated using a quadrature of the flux and making use of the point values as quadrature points. The integration in time employs standard Runge-Kutta methods. We show that this generalization of the Active Flux method in two and three spatial dimensions is stationarity-preserving for linear acoustics on Cartesian grids, and present an analysis of numerical diffusion and stability.</p>