The dependences of carrier multiplication factors M on the voltage applied to p-n Si junctions with an avalanche breakdown voltage of 10–3000 V are considered. Analytical expressions for the approximation of these dependences for electrons, holes, and generation current are suggested. In the range of varying the multiplication factors of 1.01–3.0, the relative rms error of approximation (M−1) is several percent. This is more than an order of magnitude more accurate compared with the approximation by the widely known Miller-Moll expression. It is assumed that the analytical expressions of the form suggested will be suitable for the approximation of dependences of multiplication factors on the voltage applied for most semiconductor materials.