[en] Irradiation of Si³N⁴ films on Si (MNOS devices) causes photoconductivity due to the production of electron-hole pairs. Since there are extremely large numbers of both electron and hole traps in Si³N⁴, this photocurrent is difficult to observe, but can result in charging of the Si³N⁴-Si interface. Solutions of the photoconductivity equations including diffusion, recombination, drift and trapping of the electron-hole pairs are presented and compared with experimental data on the charging of MNOS devices under irradiation