The semiclassical Boltzmann equation for electrons in semiconductors is considered together with the parabolic band approximation and interaction terms for elastic scattering with acoustic phonons and inelastic scattering with optical phonons. Taking only scalar and vectorial moments into account, two sets of equations are derived from the Boltzmann equation: spherical harmonics equations and equations for full moments. The equations are solved for two simple processes in an infinite semiconductor in a homogeneous electric field. The results show that both moment systems agree, if the number of full moments exceeds the usual choice of hydrodynamical models.