Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Si VIII. The configurations used are 2s 22p 3, 2s2p 4, 2p 5, 2s 22p 23s, 2s 22p 23p, and 2s 22p 23d giving rise to 72 fine-structure levels in intermediate coupling. Collision strengths are calculated at four incident energies, 20, 40, 60, and 80 Ry. Excitation rate coefficients are calculated by assuming a Maxwellian electron velocity distribution at an electron temperature of log Te(K)=5.9, corresponding to maximum abundance of Si VIII. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10 8-10 14cm -3. Relative spectral line intensities are calculated. Proton excitation rates between the lowest five levels have been included in the statistical equilibrium equations. The predicted Si VIII line intensities are compared with SERTS rocket observations of a solar active region and SUMER (SOHO) observations of the quiet sun.