The intensities of Si X-ray emission spectra of Si, β-SiC, stishovite, and β-cristobalite crystals are calculated. The wave functions of the initial and final states are obtained in the framework of the density-functional theory with the use of the norm-conserving and ultrasoft pseudopotentials. The all-electron crystal orbitals are reconstructed from the one-electron pseudowave functions. The probabilities of X-ray emission transitions are calculated by reconstructing the all-electron orbitals in two different gauges, namely, the length and velocity gauges. The calculated intensities are compared with the experimental spectra and the partial densities of states.