GaNxP1-x and GaNxP1-x-yAsy highly mismatched alloys (x ≤ 0.025 and y ≤ 0.4), promising candidates for intermediate band solar cell applications, were studied by optical absorption in a broad temperature range. Incorporation of N to a GaP matrix results in a splitting of the conduction band into two E- and E+ subbands forming an intermediate band gap. The analysis of temperature dependent absorption measurements of GaNP within the band anticrossing (BAC) model framework shows, with the assumption that the N-localized level position is independent of the temperature, the intermediate band position does not vary significantly with the temperature. At the same time the position of the valence band remains virtually unchanged by the incorporated N in GaNP. Subsequent addition of As atoms into GaNP allows for a shift of both valence and conduction bands, what is seen in the BAC analysis of GaNPAs absorption spectra, making it possible to tune the band alignment of GaNPAs-based solar cells. The analysis within the BAC model allows also to show the thermal shift of conduction and valence bands independently.