AbstractA density matrix approach is described to calculate the complete ohmic magnetoresist‐ivity tensor for a non‐degenerate and non‐polar semiconductor with isotropic effective mass. The conventional methods using the Boltzmann transport equation cannot be used in a satisfactory way with magnetic fields of arbitrary strength. The presence of a magnetic field in a crystal introduces some non‐diagonal elements of the velocity operator, which could be averaged properly by using the density matrix. The results obtained agree with those obtained from the Boltzmann transport equation in the limit of low magnetic field including the value of zero.